I know I might get flamed for this but I'm going to have to say Ubisoft Montreal because they have been putting out some top notch games and redefining sand-box games for the last few years (Farcry 3 Assassin's Creed 4)
I personally love Telltale. Not saying they are the best developers or anything, but I just love everything they make lately. The new episode of TWD was so incredible. --- XBL- cheezedadada PSN- cheezedadadada PC, Xbox One, PS4 and handhelds. Yay for options.
Smilebit. Y'all don't know it but they have secretly gotten back together again and are working on follow-ups to Jet Set Radio, Gunvalkyrie and Panzer Dragoon. MS spent their money wisely on this one. (Delusional fantasy over)