10 Notes
Single target Long Range
High attack speed
No crowd control
Your bread and butter unit for the early waves - because of their long range range and high attack speed, they can reliably "spawncamp" low level enemies, eliminating the need for Area Of Effect damage.

15N
Triple shot Medium Range
Average AS
Some CC
Because of their medium range, you have to get right up in enemies' faces to land all three shots, however, each shot has some knockback to it, so you can try to position the gingers so they hit multiple enemies and knock them back to the spawning point.

20N
Single shot with AOE on hit LR
Average AS
No CC
Because of their high damage and average attack speed, mages become useful once you can reliably 1-shot enemies. The AOE is is not terribly good, as enemies tend to move in konga lines and not stack in one spot.

SPOILERS AHEAD.

10N
No attack
Constant heal when idle
No CC
Healers are basically medkits - when your other units get injured, healers transfer their own hp to them. Healers cannot heal each other, so their role is to sacrifice themselves so other units can live. There are only 2 ways to keep them alive: either via level-ups (unless you already have max level College of course) or by eating bacon from the butcher's.

25N
A shot that pierces through enemies, but can only be fired horizontally Extreme Range
High AS
Universe destroying, pancake eating, face melting CC
By far the best unit in the game - once you get your head around the fact that you have to be on the same row as your enemy, these badass pensioners will carry you all the way to victory with their interrupting and knocking back shot that guarantees stunlock. Best way to use them is running up and down the map, lining up their railgun staff shots with the three lanes the enemies are coming from (assuming you don't yet have the upgrades to spawncamp and/or it is late game and you cannot keep up).

30N
A burst of shots that can change targets as they die MR
Average AS (cooldown between bursts)
Little CC
If it wasn't for their medium range range coupled with embarrassing hitpoints, ninjas could have been useful. Unfortunately, they die way too quickly and the knockback on their shurikens is way too small.

35N
Shot that does AOE damage and raises a zombie if target dies under the effect of it LR
Above average AS
No CC
Zombies stack up to a max of 6 at the from of your party, and there are 2 uses for them: as a meat shield, or a battering ram. The latter is particularly useful against chargers, as 3-4 zombies can one shot them.

30N
Reflects enemy attacks
Infinite AS
No CC
Extremely useful if you are using long range units, as they can facetank enemies, allowing you to stack squishies at the rear. Can be healed with bacon from butcher's, making healers obsolete (if you are good enough to position correctly).

30N
Weakens enemies with basic shot, places a slowing idol on crit LR
Aboove average AS
Top tier CC
Shamans benefit tremendously from levels, as nearly every shot will place a slowing totem at max lvl because of the critical strike chance increase. Keep in mind that the slow also applies to enemies' attacks, so hitstunning is even easier now.

35N
Single target shot MR, build a turret when idle, turret is LR
Average AS
No CC
Useful if you are facetanking in one place, useless otherwise. Turrets could use a longevity buff, at the moment you can barely keep 2 at the same time.

35N
AOE single shut stun MR, AOE damage nuke Point Blank
Average AS
Potentially great CC
Only useful if there are stacks of enemies present, very hard to get him to go for the melee nuke without getting hit.

40N
Single target shot MR, after 3 shots throws his sword that deals multiple hits and changes targets as they die MR
Above Average AS
Little CC
If you can out-DPS the enemies, these guys are great, otherwise they get hung up on the sword throwing animation and get hit. Are pretty self sufficient, as the sword throw knock back is enough to hitstun if there are 3+ knight present.

30N
Randomly appears in survival mode
Single target shot MR
High AS
No CC
A shooter that stays at the front of the party, a literal meat shield. Useful if you are willing to bring healers along.

"Every time they get hit, it grants you a temporary speed boost. Not only that, but the lower it HP is, the faster they fire and the more damage they deal.

So its a good idea to let them get hit once or twice and then try to keep them alive, as they'll dotons of damage." Thanks Hammerfan!

15N
Find him in the Fire Goldem stage
Single target PB
Average AS
No CC
Flails around. Totally not an octopus. 100% gimmick.

40N
Appears in escape mode at the 3000 2000 meter mark (thanks Mara and Medoragent!).
SIngle target bullets High AS LR, single target rockets Average AS LR, fires only when idle for ~1 second.
No CC
The king of facetank, but pretty useless in later levels, as the 1 second setup time prohibits dodging.

2+ archers, 1+ mage, 0-1 healer
Stay at the far right of the stage and watch the minimap. Try to snipe enemies as they come.

0-1 necrmancer, 0-1 tank, 0-1 healer, 1-9000 wizards
Depending on your playstyle, either support your wizards or just obliterate everything in you path.

1 shaman,1 tank, the rest wizards
This is what you need for night and day 2

1 tank, engineers or shellrazers rest
Sometimes you might have to switch lane. Gets bodied by beholders.

Other people's comps

1 dwarf, rest wizards
By Kaese
"(Dwarf's) high range single target stuns help so much with the stuff that got too far past you. Just makes wizarding so much easier, when baddies got past and are about to shoot at you while you position yourself, *bam* stunned and you shock em to death. (Dwarf) also acts as a good front tank."

2 Tanks, 3 Dwarfs and 2 Shamans/4 dwarfs, 3 Tanks and 2 Shamans
By AdamH_NZ
"Basically a melee build, dwarfs use their close combat move while tanks are reflecting everything back at the enemy, pretty sure you could put anything in the shamans' spot, Necros might be good."

3 Dwarfs, 2 Black Mages(recommended but can be swapped), and 4 Shamans. (Requires Day 2 unlocked and the red star party level. If not unlocked, remove mages and 1 dwarf.)
By TheFlyingTimbus
"This build works amazingly well for the entire duration of the game. The Black Mages are really just for an extra damage output and a backup in the chance that you get a big group of enemies you need to deal with, and can be swapped out with any other unit, but it's what I reccommend. Shamans are a great support as well, as they slow and weaken enemies with their totem poles, as well as dealing a good bit of damage. Dwarfs compliment the totem pole, as any of their attacks will stun an enemy. By the time they recover, they are being slowed by the totem pole to the point where they are hardly a threat. Very useful for taking out harder enemies and bosses."

2-3 Ninjas and rest engeneers
By AnsonMyPants
"i beat the main 20 levels fairly easily with 2-3 Ninjas and rest engeneers. I made a row of turrets from top to bottom in a straight line. keep the turrets just forward of the shops for stages 1-18. At stage 19 bring the turretsback at a "V". as if it is pac-man going to eat the enemy or something like that. That way when the boss level starts your turrets keep shooting the bombs at him But make surre you "yourself are between the turrets and the boss. Also at this point is to make sure you have plenty of extra notes, just keep giving yourself (and your turrets) a damage boost.

I will try some other set-ups to see if they work better, but that one seems to work everytime just perfectly."

3 Dwarfs, 3 Shamans, 2 necromancers
By Phantasm-0
"start it out by just using both of your necromancers till your zombie count hits 6, during wave one, then focus on getting your shamans up and finish off with your dwarfs so you have a wall for your dwarfs to spam hammers from behind as your necromancers maintain the wall and shamans keep them slowed Use your zombie wall as a sacricial battering ram to auto kill most bosses or the more pesky enemies like beholders, when you've got your damage song capped out"

Look for more builds in comments.

Have fun!