It totally depends on what you enjoy (and being new to the game, this may or may not be known yet). The first choice you have to make is whether you want to heal or dps. That decision will limit your class choices. If you decide to dps, you have to decide melee or caster/hunter.
Some people will argue for specific classes, but truth be told, you can pick any class, practice practice practice, and be able to get at least 2.2k rating (which won't matter as much in 5.2 anyway with the change to gear requirements). Play what you enjoy most because it will take many days of playtime to learn not only your class, but the other 10 as well (which is just as important).
If you have any questions regarding specific classes, feel free to shoot me a message and I'll do my best to answer them. You should also check out ArenaJunkies.com for PvP discussion/tips/streams.
Yeah man, pick whats fun. You can be good with 99% of the specs out there, it's just the skill level for "x" class is very low compared to "y" class. So just pick something fun, and keep playing, and watching videos and such if you wanna get better