Usually I play as many different roles as the game will allow me to have character slots for. I try to get in a melee, ranged, caster, hybrid and maybe a healer class if possible. I do this so that I can learn all the strengths and weaknesses of each class which will hopefully give me a better understanding of pvp, as well as when someone is really on or off their game when grouping or raiding. I feel playing as many classes as possible really allows you to get a fuller understanding of the game mechanics.