Bioware gets my vote. It's hard to argue with Bethesda's complete openness and exploration, but there's nothing to focus it making it feel dry and lacking of purpose. Their characters and NPC's are rediculously (sometimes hilariously) unconvincing, as well.

With Bioware's stuff, I actually feel incentive to move forward, and replay. I'm also far more driven to interact with characters, rather than just pushing through those sequences as fast as I can. Without that engagement, I can't go with Bethesda. The only thing I think Bioware could learn from Bethesda is to at least show some appreciation for open-world environments, exploration, and of course, technical quality.

I do have to put a word in for Lionhead, though! Despite the slightly patronizing obviousness and excessive humor of Fable 2, they showed an impressive sense of charm and beauty in their art design that I think more RPG's should include. They seem to know what matters and what doesn't when it comes to pleasing the eye, and that on it's own can keep you coming back for more.

(edit): Wow, I just realized how old this thread is. I found it in a Google search, so I wasn't paying attention... oh well, call me a necromancer.