I've played all three classes, and while my Warlock was my first and will always be my favorite, I have to think that Titans are the most fun to play with. Give him a AoE ground pound, slap some Ruin Wings on that bad boy, you're gonna have a lot of fun with it. Defender is also pretty fun once you get weapons of light, because everyone loves you for making the boss fights go faster. The only thing I don't like about them is that they aren't good on agility or recovery.