what class in WoW are the best for a PVP ?

For lower level pvp, pick a hunter - as a hunter with its pet is like two players combined. But for endgame - I guess most classes are viable, it is a matter of who is playing the character and how much does he know about his and his opponents' classes. Being aware what your opponent might counter your attacks with will give you a better understanding how to defeat and overpower them.

the best class is a... MAGE! i played a mage on nathreizm lvl 70 and i pwn dont meen to brag but anyway there good cause they can freeze people and run and shoot... best spec for a pvp mage would be frostfire for instapyro and etc

We all know, and have probably heard this a lot of times, that every class is the best in some ways, although I agree some classes have slight advantages over others such as armour, health, range dps and so on. I personally play a hunter and warlock, and have saying that, I believe that hunter and lock "pwn" in pvp because of their incredible damage and burt damage as well as the range dps. For hunters, pets are very good and for locks, both pets and healthstones to heal themselves are very good aswell. What I like about locks is their "drain soul" which heals you for quite reasonable health.