Warlock - I'm mostly addicted to Osmiomancy Gloves. This build is even better after the buffs/fixes to Coldsnap Grenades and Iceflare Bolts.
Titan - hard to beat a good Sunbreaker build. I've been alternating between Synthos (which I find more personally useful) and Phoenix Cradle (when I want to be a better teammate). Honorable mention for Sentinel with Bastion because everybody loves overshields, but I haven't finalized a build yet.
Hunter - Gyrfalcon with Telesto makes a better combo than most people realize. Because of the charge time and the delayed detonation from Telesto, volatile rounds are extremely easy to keep up.