I play as a Titan and pretty much dominate majority of my games. Strikers pretty good, with the Shoulder Charge you can get the drop on enemies. Strikers Super can get multi-kills and post mortem kills if specced properly. Defender is really for supporting teammates by giving them cover and providing them with orbs. Hunters are really poweful in terms of abilites for PVP, the golden gun is an insta-kill for 3 people, and Blade Dance isn't exactly easy to counter. Warlocks are okay, I haven't seen any spectacluar use of their abilites to be honest.