Well, the oldest I have is Final Fantasy for the NES. I still like to play Final Fantasy 2 (4) for the super nintendo since it's a classic, but I usually play it for the ps1 because my power adapter is broke on my SNES. I get regular use out of my ps1 for games like Xenogears, Shadow Madness, Final fantasy 7/8/9/tactics, Suikoden 2 and legend of the dragoon.
As far as games that have stolen the most of my life (100's of hours each):
Baldurs Gate 2
Icewind Dale 1 and 2
Morrowind
I'd put WoW and FFXI, but it's expected of MMORPGers to steal the life out of their subscribers.