Straight PvP servers are going to be populated by the lowest form of internet scum around. Straight RP servers are generally going to have a bunch of elitest assholes. PvE servers are going to be kind of a mix between both from my experience and RP/PvP servers offer a fun mix of roleplaying while still keeping you on your toes in regards to being stabbed in the back by an opposing faction at any moment.
In the end, you should scope out the realm forums a bit (but don't pay too much attention since we all know what internet forums can turn into) and make yourself a character on different relms to see what the atmosphere is like.
Other then that, it's all a matter of finding out what you will enjoy playing the most... as opposed to playing "teh most 1337 evar" race/class combo. Trust me, someone who enjoys what they're doing will whip the shit out of just about anyone playing the most tweeked out character simply for the perks.