The hybrids strike me as more powerful than any other classes on the PvP server... here's my take on each class:
Beastlords: Pet DD while the beastlord debuffs and DoTs. All in all, the only bad thing about them is lack of a snare. Self-heals aren't large, but you can play pet cleric (and with the AA, you can have your pet snare the target and kite while your target beats them).
Berserker: I'm really not sure how their ranged dps holds up to a Ranger's, but Berserkers also get nifty skills using their axes. Stuns, snares, decent defense, and good offensive melee dps... with the Intimidation skill, you might even be able to reverse-kite players. Not sure.
Cleric: Decent against the low-damage, fast-hit classes. Stuns are one of the only problems. Basically, dual-wielders get screwed over by the cleric's repertoire of defensive "procs"... Ward of... spells. With the right aas, and decent gear, I think that a cleric would be good in PvP.
Paladin: Stuns, self-heals, and a 2-hander (or one-hander and a shield if facing a caster, for bashes), plus the ability to root, good hp, etc...
Rangers: Self-heals, fast melee dps (kinda a bad thing... any dual-wielders are going to have issues against damage shields and the cleric Ward line), decent ranged dps, snares, debuffs, DoTs.
SK: Taps, snares, DoTs... same weaponry as the Paladin (2h or 1h and a shield for bashing casters).
Necro: Taps, snares, nukes, DoTs, and pets. Plus Fear. And Fear is good.
Enchanter: I think Enchanters can mana drain, can't they? Good against other casters. Rune, debuffs (slow), and crowd control would be decent against melee classes.
Magician: Nuke the hell out of something while your pet wails on it. Use the air pet for stun procs.
Wizard: Snare/root and nuke the hell out of it =p
Shaman: Debuff, DoT, sic your pet.
Druid: Debuff, root-rot, or kite.
Warrior: Kinda gimped, imo... no spells for healing/debuffing/etc... good armor class (good against meleers) and hitpoints... good sv magic... but other than that, I'd say they're -very- gear dependant.
Monk: High dps... bad against damage shields, imo... relies on gear, same as a warrior.
Rogue: Poisons are the fallback for the rogue, to separate it from other melee classes. Gotta learn to strafe-turn to stay behind the opponent.
Bard: Decent melee dps (no double attack until 71, though), nuke/debuff/dot/damage shield/snare/charm/mez songs. Jack of all trades, I'd assume they're very good in PvP.
My two cents.