Well, here we go
GURPS, because I can do anything with it, and it's easier for me than HERO. Besides, I like bell curves in my dice spread!
BRP, especially China, because it goes fast and it's almost as versatile as GURPS. It's also easily customizable.
WFRP, because I like career and lifepath-based character creation. It also has a very cool setting. Of course, same goes for Dark Heresy, and lots of other systems, but this one is the most popular one.
UA2, because it always gives and takes at the same time, you always have to make some exchange when your character advances. I kind of like that. I also like the madness meters.
The Riddle of Steel, because it makes you answer the riddle if you want to play and have fun at all. It also has a very cool system, even if a bit crunchy.
Exalted, because it has a cool setting with lots of references to existing mythologies. Creation needs you, too! That one is despite the system, though. It has its own kind of cool moments, of course.
I'm sure I forget some system. But then, nobody's perfect. Yeah, not even me!
Some of us just come closer to it