Currently, GURPS 4th Edition is my favorite; sometimes even for running some D&D settings.
Oddly, once I tried it (GURPS,) I was surprised to learn that I found the game which everyone decried as being super complicated to actually make more sense to me and be more intuitive than many of the D&D rules.
I still like D&D. There is a lot of fluff material and available material that I highly enjoy. I'm just not always crazy about the mechanics. In particular, once I experienced a game in which I had active defenses, it was hard for me to go back to the d20 vs static defense AC way of doing things.
Star Wars: Edge of The Empire is a game which pleasantly surprised me. I'd say it's currently in my top 5. I don't have enough experience with it yet to make a more long lasting declaration as to my feelings toward it, but, so far, I really enjoy it. While it's not my #1 favorite, I highly enjoy it, and have stolen a few of the mechanics to use in other games.