If Nostalgia were the defining feature here, I would have to go with the Genesis. I loved playing Golden Axe, Altered Beast, and so on in the arcades, but never owned a Genesis. I wanted what I couldn't have I guess. Now it gets way more love than my other consoles, particularly those Sonic games, as others have mentioned. I rarely touch Mario games, even though I own mostly Nintendo consoles.
However, I must admit that if Quantity is the defining feature here, my poor N64 is falling apart due to over use and sheer abuse. After school on Fridays, the friends would come over and we would play until we couldn't wake up Saturday morning and resume. It was just the console that offered the best bang for multiplayer, and hit the sweet spot for me in terms of age, social playability, and free time.
