hey i;ve just started playing wow and I want to either roll as a human paladin, a human hunter, or a human shadow priest and I was wondering which is the best for pvp? arena's one on one's battlegrounds... whatever, it is it will become my main thanks for your time.

First of all, hookedonphonics.com

Second, choosing a class based on how powerful it is at the moment is stupid, since classes are constantly changing and whatever is most powerful won't be in the future.

Try all 3 classes and stick with whichever one you enjoy the most. All of them are historically very viable in arenas and battlegrounds.

Personally, I enjoy the Discipline Priest for PvP. Shadow Priests are very squishy for Random Battlegrounds, where no one will keep an eye on you. Focuses on DOT damage (damage over time) and has some powerful channeled spells. Weak against the Hunter and rogue, as Shadow gets a move to slow down incoming enemies. Also weak against multiple enemies, unless you tab DOT spam.
The hunter is very powerful, and are the best soloers in the game, with very little downtime between fights. Very handy in Random Battlegrounds and arenas, but pitiful at one on one, as any idiot will know not to attack the pet, but to hit and kill you quickly. Weak against the rouge and most plate-wearers.
Paladins, at higher levels, basically become flag running gods, with Holy being the best. Need a durable flag runner? Say hello to the Holy and Prot Paladin. You are, however, over looking a few very good PvP classes. Weak against almost nothing if played correctly. Very easy to play incorrectly, however.
First off, the Rogue. A PvP god at low levels, at level 10 you obtain the ability to instantly appear behind your opponent, with extra damage, allowing you to one-shot almost anyone. Even at higher levels, you turn invisible, and people start dieing. Battleground and Arena gods, but near useless at one on one. Weak against plate-wearers.
The mage is very fun at higher levels. Once you obtain the Mirror Image ability, you have your own little group that can blast your opponent while you run away. Weak against the Hunter, the Warlock, and the rogue.
And the Warlock. Basically a fusion of the Shadow Priest and the Hunter, they have demon pets that can act like rogues (Sucumbus), tanks (Voidwalker), ranged damage (Imp), and...something (That demon dog thing). However, they do not need to tame or feed their pets, or even level them up (I think). It focuses around pet control and DOTs to defeat your enemies. Weak against the rogue, plate-wearers, and the mage.
And last, but not least, my personal favorite, the Death Knight. A plate-wearer, they are durable, with a nice selection of specs and abilities. Able to tank, deal damage, or become a pet based class, this is my favorite class of all time. However, you need to have a level 55 character to make a level 55 Death Knight. Weak against almost nothing if played correctly, but also very easy to play poorly. The mage and warlock are its general attackers.

REMEMBER! No class is all-powerful. Each patch changes the standings. On the other hand, a correctly played class with friends can be near unkillable, no matter what kind of class it is. And every single class has its role. None of them are useless. If you find one of them to be really bad, either you need to change classes, or your doing it wrong.


EDIT: I forgot to mention that you should not try to level up on PvP. It is very slow and can get very frustrating when you hit a row of bad games/teams. All classes are viable for PvP, as well as all specs. Each just plays a little differently.