I'm a bit of an old fart. I've been playing for 26 years and GMing for 26 years.
D&D 3.5, Old World of Darkness, 7th Sea and Midnight are my favorites. I also like the other editions of D&D (except 4), Pathfinder, RIFTS, Shadowrun, Cyberpunk, HERO, MektonZ... and a bunch of other I can't think of.