1v1 - Lancer
5v5 - Berserker
gvg - Sorcerer
But in all seriousness - they're all good depending on what you're doing. Every single one has its place.
What I have noticed so far is:
Lancer 1v1 is very strong because basically you wait for your opponent to blow all their cooldowns (and block it all) then do your moderate burst. It's a character that takes patience and waiting for the opportune time to attack. Very hard to kill a lancer.
Warrior is all about positioning and dodging. I am currently playing a warrior and haven't really made up my mind about them... I love the mobility that comes with a warrior!
Mystics and Archers have a WICKED DoT that kills melee classes. I will be pvping and all of a sudden my health bar goes pink and disappears! Plus Mystics bring so many group buffs and heals to the table- if I decide to play a ranged class Mystics will be the first to try out.
Priests with their heals are almost impossible to kill. You have to continually stun them to even get a chance, and I watch them just keep running away self healing and giggling... Not cool.
Beserkers is all about timing your big hits. I also played a Beserker in CBT3 and 4, and I like the block, but found it hard to land the big hits.
So, if I can't get Warrior down to a fine art I might try Slayer (good mobility and better self healing) or Mystic (which is kinda like a healer/lock combo).
From what I've seen playing a ranger, Lancers are very very hard to beat 1v1. They don't take much damage, and they can do some decent damage as well. The other crazy one that I've seen is the Sorcerer. They're pretty squishy (if you can catch them) but the big thing is that they'll kill you in a couple seconds through their insane damage.
lancers are the easiest class to 1v1 with.
mystic 40+ skills do nothing against block. later on mystics are too squishy to even stand a chance against warriors and slayers once they get backstab(which ignores slows), and are usually killed quickly against sorcs if the sorc plays its cards right. their dot doesn't scale with gear so they're out of dps options at higher levels.
priests can selfheal while making themselves un-debuffable. as long as the priest plays carefully, unless the enemy has no way to regain lost health, nobody wins
warriors have backstab which stunlocks the target which mean all cloth-wearing enemies will probably die before coming out of the stun (priests can become unstunnable so you have to take them by suprise)
archers bad against enemies with block and enemies with more ranged dps
What kind of play do you want to do, that's how you pick a damn class. ALL classes have their angles, anyone who say's "blah I beat ALL, so play my class" is a failtard or just as bad a basic troll.
Play what you enjoy, and enjoy the game, winning or losing. If you can't do that, then you'll never be happy playing games, which means you should quit.