Best Soloing Class : SWOT - Higher DPS than VHL and can kill bosses faster, but it's can't sustain HP as good and it can't kill all the bosses in the game + it's hard to use)
Best Farming : Vampire Lord - Faster than Blaze Binder, that's all there is to say
Best Support : Stonecrusher - Can sustain the team very well, it can buff their damage by quite a bit and can prevent people from dying easily.
Best DPS : Chrono Dragonknight - Highest DPS in game can be achieved from this class, but it needs support to stay alive
Best Tank : ArchPaladin - it can kill almost every boss in the game, the reason why it's not the best soloing class is because it kills slowly
Best PvP : I don't pvp much but it's probably VHL/Dark Harbringer/ or Evolved Shaman
Best Dot : Infinity Knight/SWOT - Both classes can hit insane dots, the reason why I have included dot classes, is because they can dish out crazy damage on mobs if the room is glitched.
Best Overall : VHL or SWOT - VHL is the best class for free players, it deals tons of damage and can manage itself very well against pretty much all bosses in the game. SWOT is basically a pay to win version of VHL, it has higher damage than VHL but less sustainability. The only thing SWOT can do that VHL can't is farm high hp mobs very quickly.(Especially if the room is glitched)
Hopefully this sums up all the best classes in the game in each category. Feel free to make any make any points if you don't agree with my list.