I used to love TES4 too, but after playing Daggerfall and Morrowind, I started to look at Oblivion coldly. The old concept of Oblivion was great, but what was released… meh. But hey, quests in Oblivion are pretty good.
I don’t think I have any favorites, there are too many great games to determine the best game, well… VA-11 Hall-A. It’s one of the few games that really touched me and affected my emotions deeply. Also, I love this game ost, one of the best game soundtracks ever, imo.