My vote goes to Bethesda.
Seriously thousands of hours played with Oblivion. So many characters. No fast travel plays. Magic characters/stealth/strength. I've played this game from start to finish so many times since 2006 that it has to be my most played game of this gen.
Fallout 3 is a very close 2nd for total time played. One of these days, I will get those Silver Tongued Devil and computer hacking trophies.