Just like there is a lot of music that sucks
So that being said I do have my favorites and I will list them by genre.
For the "Hard" Sci Fi category I elect Eclipse Phase. I'm really digging Eclipse Phase. A Lot. It's definitely one of my faves.
When I think of Horror I think of this obviously...
Fantasy? Dungeon World hands down.
Supers? Man I loved this game, wish I still had a hardcopy.
Generic System? With a Hat Tip to Fudge...
This list could go on and on. If I had to pick one game that has shaped who I am today though, I'd be remiss if I didn't say Cyberpunk 2020.