All the classes can perform well in PVE and PVP, but some are harder to master than others.

Here is a simple statement of skill required Tier list :

S tier : Reaper
A tier : Summoner, Spellsword, Berserker
B tier : Spearman
C tier : Bard

The one you will struggle the most in pve leveling is by far Reaper, and the no brain mode will be Bard, the biggest difference is between S tier and other tiers, all others tiers are closer to each other in term of difference.
There is very particular situation where even if Summoner is A tier and hard to master to get 100% efficiency out of it, it will be almost no brainer to for leveling.
Berserker is also quite easy in term of survivability, as sword master is.

In fact im more talking about how hard is the class to master, everyone should be able to figure out how to solo basic content with any class, game isn't that hard at all.

So basically, there is three role DPS TANK HEAL.

for Tanking you got choice between Berserker and Spearman

PVE TANK
Spearman seems to be the most liked and efficient for pulling (most players claim it has a most efficient pulling than berserker) Tank in PVE at the moment, but berserker Tank shines in very specific instances and has more damage output while tanking.

PVP Tank class related.
Berserker is way more present in PVP Leaderboard than Spearman.

for Healing Bard Reaper and Summoner just works fine

PVP HEAL
The rank 1 team in pvp uses Summoner healer
There are several teams that performs nice with Bard and reaper Healers.

PVE HEAL
Again all the three healing class just works fine at the current state on any kind of PVE group content.

For DPS you can play all the classes because all classes have a DPS role between there two masteries. Bard will be the easiest for ranged DPS in dungeons with other players to have a decent damage output, its also a good healer.

There are no DPS class that will be rejected from any content, that the beauty of this game.

for pvp check the Leader board going down right of your interface to Museum of the continents > Book of Aeons > click on the small shield with a star > Disputes > Battle Squad Ranking .

I decided to focus on 3 class because it's the right amount of time for a hardcore player.

why?

- it allows you to get the in game currency cosmetics from events quicker
- it's the only way to be able to play all roles (RANGED/MELEE DPS TANK HEAL)

i personnaly started with reaper / summoner / Berserker, and then when i'll finish them i'll make a spellsword, and then when i'll have fulled everything a spearman and bard.
My choice was determined by pvp leaderboard as i love pvp.
If you prefer pure PVE i'd make a spearman over a berserker.
You can also switch summoner and reap with bard and spellsword.
i'd recommand just having a comp that allows you havin MELEE/RANGED DPS / TANK / HEAL, so you can face any situation.