I dont really have a favorite, though the company i trust the most would be Valve. They made the beautiful Steam application and a whole bunch of great games (I'll look past Dota and Dota 2 for the purposes of this post). Others are good. Bungie is smart, but never captured me with any story thus far. Bethesda is generally good, but often come out with a great incomplete game (see: Skyrim's bugs) and I enjoy Bioware because of Mass Effect 2 and most of 3. However Dragon Age was a flop for me and ME1 was dull.
Generally though, Valve delivers at a low cost (Which is important for me) and high quality (even more important for me). Plus, to show dedication, they've released hundreds of updates for TF2 (released many years ago). They actually just added about 50 hats to the game a bit ago. When they set out to focus on gameplay (L4D, TF2), they do amazingly. When they set out for story (Half Life 2), it's enough to make me tear up almost.
So yeah, I have to choose Valve on this one.