Gona breakdown some classes that i tried not at 60 yet tho:
-Hunter : as stated above, really fun and good, you have a chance to figh twink rogues with ok gear that you can get through dungeons easy
-Druid : shapshift cost too much mana wich is a deal breaker for me, else i would play them, they are full of tricks and macros you have to use aswell,
-Paladin: as retri is boring, slow atacks, not that good damage and you get kited for days by any ranged class that knows what they are doing. As holy is fun if you manage your bubles/ cds well.
-Priest: Shadow is kinda boring for me at pvp, even if they are strong, if an hunter viper stings you, you are oom in 12 seconds, if they dont, you are oom anyways if you, like me, like to support the team with some heals
-warlock: only tried as affliction, it is good, you dot people up, you have no real burst unless they let you cast freely wich wont happen much, fun if you like to do huge damage but spreaded across everyone, you are also a fear machine wich i dont enjoy much but is powerfull
apart from this i suspect that rogue is the most fun for world pvp and low scale pvp (WSG), while elemental shamys being super fun in huge battles (AV) if you like to spam chain heal/ chain lighting, but totems can be a deal breaker for you since totem twist is such a HUGE deal and is only fun for your group