NES the GoAT of course. Then it's a tossup between PS2 and 360 for the number 2 spot. My personal library for both systems is about even.
Still got some fond memories. Released when I was 21, PS2 was my first adult console. About 8 of us went down to the game store on release. They held a lottery and one of our numbers was pulled, so we stayed up all night and the next day playing Tekken Tag, SSX, and Midnight Club.
Some really unique titles that are all time favorites. Mister Mosquito, Katamari Damacy, State of Emergency, Spyhunter. XIII is probably my favorite first person shooter outside of the DOOM franchise.