Well, i didn't play RoTK 11 (some players say it's the best), i just played RoTK 13 and most of the historic TW. But here to help you decide a short comparison between TW3 kingdoms and RoTK13 (i can't fully compare to 14, i just started to play it !) :

Total war 3 kingdoms is a Total war with an ancient chinese style and look. It's a great Total war but it's a Total war. Every Total war is about a specific time : medieval Europe, ancient Rome, 3 kingdoms, medieval Japan. While Koei "RoTK" games are all about 3 kingdoms.
If you have played another Total War, you won't be disoriented by this one.
You alternate between real-time battles and the campaign on a large map divided into multiple factions, you can recruit troops with gold, according to the level of the buildings in your city, buildings that you can improve.

RoTK serie specificities :
In RoTK you slowly upgrade your cities by assigning governors to them. These governors are historical characters with stats that make them more or less capable of improving agriculture, commerce or military. Every turn this city improvement is slow but automatic, but some administrative tasks can really be repetitive.
Another difference is that when you raise troops, it's fully related to what each governor was able to raise in each of your cities. You're not just limited by your total faction money and your barracks level.
Lastly in RoTk, historic events trigger as you progress through a chapter and fulfill some specific conditions.

Notable food supply management differences
Total War : every region produces an amount of food depending on your farms level and farms related buildings. The food balance is managed at the faction level. You can have a drastic shortage of food in one region as long as another of your regions produces a lot of food.
RoTK13 : Your army consume food when on the road between two cities or besieging a city. So if you've multiple huge armies and are besieging the enemy capital. And another enemy capture one of your "minor cities" on your back that used to be your main granary, then you're f*****. Because then your armies will disband in 10 days instead of 2 months. (cf. maybe 2010 drama told an event of this kind, Cao Cao raiding Yuan Shao's little granary city by night)
RoTK14 : Supply has been simplified from 13, an army that is deployed consumes a certain amount of food after a while from the city from where it was deployed and loses morale and starts to disband if supply amount isn't reached. However the hexagons path from the initial deployment city to the unit must be uninterrupted, so that the supply could reach it. So you must ensure that this path is continuous and you can potentially cut off enemy supply path.

RoTK13 roads vs RoTK14 hexes
All RoTK are about 3 kingdoms but it's like 2 sort of games sharing the same title.
RoTK 13 is quite similar to Total war with real time battles and a big campaign map.
Players say RoTK 14 is more like 11, as there are hexagons.
So you've to decide what you prefer : hexagons -> RoTK 11-14 / roads -> RoTK 13.
13 is more straight because there are big roads between the cities. If two armies cross each other on a road, they fight. in 14 the more hexes you conquer the more influence you have on the related city, and you can build on these hexes to assist you (for example traps, arrows towers or military camps). Two enemy armies fight each other if they are close in the hexes zone or you attack an enemy city.

Scenario mode victory conditions
After about 15h playing Sun Jian vs the yellow turbans, i feel that a weakness of RoTK14 is how you are forced to conquer the full country by stepping on or vassalizing all the other factions to win a scenario. Hmm yes, in TW 3 kingdoms, it's about the same.
But in RoTK13, each scenario had historical and more limited requirements to trigger scenario victory. So that you could just play from start to finish the whole 3 kingdoms story without having to conquer full China again and again. Well i don't mind playing conquering ancient China, that's why i'm here after all ? But if you have to do it in every scenario it might take a while ! :d

Rotk13 exemple of scenario mini-mission


Rotk14 every scenario is a starting date when you've to unite the full land


In TW3 kingdoms, you've to almost unite the full land (become emperor and capture enough commanderies)


However here is where Total War 3 kingdoms shines :
But the Total War ambiance and sounds are incredible, and i like to hear : "the enemy general is running away from the battlefield, coward !" Graphics are of course much better too. It has more interesting and varied and much less repetitive administrative tasks, and the UI including diplomatic UI is super handy.
TW3 kingdoms offers an interesting and original hero class system, for exemple some of your generals are better at duelling other generals, some are better to kill a lot of basic soldiers, some are strategists with related skills. Classes are all related to some specific colors so that it's really easy to distinguish between them on the screen. It's bright !

TW3K is famous for its battles quality and your tactical freedom


RotK13 has 3D battles but not so beautiful, you can freely move units, and trigger some special tactics but the main game is on the campaign map with army/supply management


Rotk14 battles are directly on the hexes of the campaign map (you can't control your units once engaged)


Duels
There are automatical duels on foot in TW3K. In RoTK, there are automatic duels by horse. Not that it changes much as it's automatic, but i liked a lot the 2010 drama and its duels on horseback so i was happy to see that, even strictly as a spectator.

TW3K automatic foot duel


RoTK14 automatic horse duel

RoTK is known to have :
- Some fictive and historic scenarios that tell you romance of the 3 kingdoms events.
- A sandbox mode with different starting dates related to some major events.
- An editor that allows you to customise characters and maybe other things i don't know.

Base game comes usually with some main scenarios and some starting dates.
And after that comes the power-up kit (puk), an expansion pass improving the whole game : character traits, diplomacy, etc. It's advised usually to buy at least the game + puk.
And after that you've multiple season pass that add multiple historic or fictive scenarios, and multiple starting dates for both the scenario and the side modes. The season pass are required to get a complete game telling the whole 3 kingdoms story. And that's how the game is so expensive (but don't forget it's an expensive high quality game) :-(

The english official description of content is really imprecise. So after having hesitated several hours and if you wonder too which edition to buy, here are some more details.

https://store.steampowered.com/app/872410/ROMANCE_OF_THE_THREE_KINGDOMS_XIV/

- Tutorial an interactive tutorial with some missions that explain the basics but not everything, there is also an in-game tutorial with texts to complete that.

- Scenario mode :
(historical)

• 184 Yellow turban rebellion (you can play as Yellow turban or against them)
  
• 190 Anti Dong-Zhuo coalition (Dong Zhuo just seized the power)
  
• 194 Warlords (Lu Bu just killed Dong Zhuo)
  
• 200 The battle of Guandu (Yuan Shao vs Cao Cao)
  
• 207 The three visits (Liu Bei visits Zhu Ge Liang)
  
• 217 Assault on Hanzhong (Liu Bei invades Hanzhong after Red Cliff)
  
• 227 Chu Shi Biao (Zhu Ge Liang advances North to conquer Wei)

(fictional)

• 199 The Han's loyal retainers (Ma Teng and Liu Bei are killed trying to rescue the Emperor)
  
• 209 The split of the Cao family (Cao Cao dead at Red Cliff, rivalities between his sons)

War chronicles mode isn't included in base game

https://store.steampowered.com/app/1427650/ROMANCE_OF_THE_THREE_KINGDOMS_XIV_Diplomacy_and_Strategy_Expansion_Pack/

- "Geographic Advantages and Outlander Cities" (you gain geographic advantages conquering each of the 17 provinces, some allowing you to negociate or subdue 5 outlander forces : Wuhuan, Xianbei, Qiang, Shanyue, Nanman)
- "Trade with foreign nations throughout Eurasia" (India, Persia, ancien Rome)
- "Traits and tactics" (choice of a battle formation raising an army ; alliance, attack request, rumors)

- Scenario mode historic and fictive events
(historical)

• 191 The intention of two Yuans (Yuan Shao and Yuan Shu's ambitions)
  
• 208 The battle of Chibi (here it is)
  
• 219 Anti Guan Yu coalition (Sun Quan aims to recapture Jing)
  
• 238 The conquest of Liaodong (Wu-Shu alliance to capture Wuzhangyuan vs Wei)

(fictional)

• 197 Emperor Lu Bu (after Yuan Shu's death, Lu Bu takes his throne and army)
  
• 201 Yuan Shao ruler of the North lands (Yuan Shao won battle of Guandu)
  
• 209 An old warhorse's ambition (Cao Cao victorious at red cliff, Liu Bei and Sun Quan's resistance)
  
• 210 Zhou Yu's master plan (Zhou Yu's final blow vs Cao Cao after red cliff battle)
  
• 212 Splendid Ma Chao takes a leap (Ma Chao defeated Cao Cao and marches to Luoyang)
  
• 235 Enduring the autumn winds (Zhu Ge Liang survived in Wuzhangyuan battle)

- "War Chronicles Mode"
190 anti Dong Zhuo coalition
199 battle of Guandu
208 battle of Chibi
218 battle for Jing province

If you wonder what is the "war chronicles" mode, here is the in-game description :

War chronicles is a mode where you try to win within a restricted time period and a restricted area. Each scenario has a term, and failing to meet its victory conditions within that term will count as a defeat. Fulfilling defeat conditions will also result in defeat. The scenario will be cleared when you fulfill the victory conditions. When you clear the scenario for the first time, you will receive a reward. The following are rules exclusive to war chronicles :
- Certain commands will be unavailable including Foreign and some Plots.
- Disasters will not occur.
- You cannot capture officers.
- Officers will not die in battle nor they will die of old age.
- You cannot obtain geographic advantage.
- Because Trade is unavailable, foreign technologies cannot be obtained.

In short, it's a simplified side mode that doesn't trigger scenario events, where the goal is to conquer the world as fast as possible to increase your score.

https://store.steampowered.com/app/1198833/ROMANCE_OF_THE_THREE_KINGDOMS_XIV_Season_Pass/

- RTK14 1st wave, 2nd wave, 3rd wave (editor)
- RTK14 difficulty modes : Veteran, Extreme
- RTK13 officer CG set (cosmetic)

- RTK14 historic and fictive scenarios :
(historical)

• 198 The Lu Bu campaign (Yuan Shu becomes emperor, Cao Cao + Liu Bei vs Yuan Shu + Lu Bu)
  
• 202 Hebei conflict (Cao Cao victorious at Guandu invades Ji)
  
• 211 Battle of Tong gate (Ma Teng assassinated, Cao Cao vs Ma Chao)
  
• 215 The battle of Hefei (Liu Bei has to return Jing province, Sun Quan vs Cao Cao)

(fictional)

• 188 A yellow sky (Cao Cao, Sun Jian and Yuan Shao joined the victorious Yellow turbans)
  
• 199 Gongsun Zan the hero of Hebei (Gongsun Zan + Liu Bei vs Yuan Shao + Yuan Shu)
  
• 251 Conflict among clans (who is the strongest clan ?)

https://store.steampowered.com/app/1431482/ROMANCE_OF_THE_THREE_KINGDOMS_XIV_Season_Pass_2/

- RTK14 watercolor painting style officer (cosmetic)
- RTK12 officer CG set (cosmetic)
- RTK14 editor 4th wave (editor option)

- RTK14 historic or fictive scenarios (main content, probably what you want)
(historical)

• 188 The wavering Han dynasty (Yellow turbans rebellion ended, He Jin and the ten ennuch's plots)
  
• 196 The rise of Cao Cao (after Cao Cao's victory at Zhongyuan vs Lu Bu)
  
• 225 The subjugation of Nanman (Liu Bei dies after being defeated at Yiling, Zhu Ge Liang south campaign against Nanman)

(additional events added to other scenarios)

• Zhu Ge Liang Northern campaign
  
• The subjugation of Southern Jing province
  
• Sun Ce pushing forward

- War chronicles (side mode content)
194 Battle for Yan province
204 Battle for Hebei
211 Liu Bei enters Shu
251 Clash of the warmongers
279 Battle for Wu

I was wondering why there was still a dlc not purchased, well some players talked about that here : https://gtm.steamproxy.vip/app/872410/discussions/0/3003303575730184447/

And it was the pre-order bonus DLC.

Historical 249 JAN The start of change

After Zhu Ge Liang's death, Shu is left on the shoulders of Jiang Wan and others, while Sun Quan's losses are beginning to take their toll on Wu. In Wei, Cao Rui defeats Gongsun Yuan and annexes Liaodong, only to die shortly after, and a discord stirs between Sima Yi and Cao Shuang, the guardians of the new Wei emperor Cao Fang.

https://store.steampowered.com/app/1198832/RTK14_Scenario_The_Start_of_Change/

ROMANCE OF THE THREE KINGDOMS XIV: Diplomacy and Strategy Expansion Pack Bundle
base game + puk

https://store.steampowered.com/sub/510898/

ROMANCE OF THE THREE KINGDOMS XIV / 三國志14 - Digital Deluxe Edition
base game + season pass 1 (on main store page, no direct link)

ROMANCE OF THE THREE KINGDOMS XIV: Diplomacy and Strategy Expansion Pack Bundle - Digital Deluxe Edition
base game + puk + season pass 1

https://store.steampowered.com/sub/510899/

ROMANCE OF THE THREE KINGDOMS XIV: Diplomacy and Strategy Expansion Pack - Digital Deluxe Edition
puk + season pass 2 (without base game or season pass 1)

https://store.steampowered.com/sub/510904/

Actually, if you're short on money but still decided 100% to get RoTK14, then the minimum is base game + puk.

However if you want the full version (for now), this is what you need :

ROMANCE OF THE THREE KINGDOMS XIV: Diplomacy and Strategy Expansion Pack Bundle - Digital Deluxe Edition (-40% 60€)
https://store.steampowered.com/sub/510899/

+ season pass 2 (-40% 18€)
https://store.steampowered.com/app/1431482/ROMANCE_OF_THE_THREE_KINGDOMS_XIV_Season_Pass_2/

+ the pre-order bonus DLC "the start of change" if you're interested of course ! (3€)
https://store.steampowered.com/app/1198832/RTK14_Scenario_The_Start_of_Change/

In conclusion i would say RoTK 13 and 14 are two different (and both expensive and interesting) games, and 13 is probably better on some aspects (really better). But it wouldn't make sense to buy twice the exact same game. So i'll just consider this RoTK 14 with curiosity.

Whatever your choice, Total War 3 kingdoms, RoTK 13, 14 or 11, wish you to have fun !