the PC. There is no competition here. Especially if you add in all the console emulators.

Games on my PC:
Grand Theft Auto: San Andreas
Quake 2 Evolved
Urban Terror
Mario Kart 64
Super Mario All Stars & World
Dr. Mario
Tetris
Civilization II
Chess
Sudoku
FreeCell
Spider Solitaire
Gargoyles (for GameBoy)
Need for Speed III: Hot Pursuit
Mortal Kombat 1-4
Super Smash Brothers
Fallout 2
1942
Super Metroid
Contra III
Bust a Move
Monopoly 64
Snow Board Kids 2

Probably some others I'm missing. Over all though, that list easily dominates any console in existence today. Also, Playstation 2 and Gamecube emulation are getting closer every day, so expect this list to keep growing.

Why do people bother wasting money on a new console? Mario Kart 64 is still probably the best game of all time anyway, when you've got four peeps around.