their is a PvP spec for each class really. each class has that 1 spec that dominates all other specs because it is better in PvP for a specific feature.
For hunter that spec is really Survival- it allows you to survive more often and gives u a shet ton of procs off traps which is what you use as a hunter regardless of spec. also the procs are very very good compaired to other hunters such as the ice trap one where if you ice trap someone u get instant explosive shot 2 times. 0 second coolddown and it's free i think. and yea this shot is fking strong. People saying Marksmen is okay/good as well i played marksmen in PvP it's alright not many good talents for PvPing really.
hunters are good at the start they are OP as fk and as they get higher lvl they tend to suck because most people who play hunter's don't know wtf they are doing, don't know how to put buffs on or take them off such as aspects, don't know what pet to use, etc..etc... this is debatable end game at 85.
Elemental shamans is really a PvE spec as they need time to cast and usually it takes long at the begging. Also most of their good talents they get endgame. and still they can still hit hard but they take time as well so either you need to know what your doing really or just have someone distract the enemies for u to hit them. Enhancement shaman is really for PvP dishes out a lot of meele dmg and casting dps as well if played correctly but this is one of the hardest classes to play. i have seen shamans own people at low lvls higher lvls i would say it is more difficult because thats when everyone else has their good skills. and most of these ppl know what they are doing or they have good gear, or just playing a cheap class that takes no skills.
If your trying to pick a class for PvP i will say go either. classes in this game get buffed and nerfed constantly to be worrying which is the best. one patch hunters might be very good another hunters can suck and mages will be good. play what u think is fun. either way PvP is Player Versus Player. if you don't know how to spec, gear, and play your character properly then you can fk the game up for yourself. PvP is pretty difficult because you can use enchants, gems, resilence gear, different arttacks to counter your oppenants, potions, buffs,etc.. not to mention most of the time you will get ganked by 2 or more ppl which isn't fair so really pick a class you find fun and learn it.