Now, I do have to disagree with people who want to claim the PC as the greatest, mostly because in a way it's an unfair comparison. For one, the PC isn't intended as a gaming system, that's just something that people do with it. For two, there isn't a definable "life" to the PC, so ancient games like King's Quest, Zork, and Gauntlet could well be called "PC" games the same as Half-Life 2 or World of Warcraft. Last, the PC isn't a static system, it has to be upgraded often (once a year or so) to play the latest games properly (and thus get the most enjoyment out of them), unlike console systems which are garenteed to play everything released for them during their 3-5 year life span.
So while I have and will continue to enjoy some of the great PC games out there, I can't feel it's proper to call it the greatest gaming system... I'm not trying to start a PC/console gaming war (as I'm well aware that they happen), I'm just pointing out that it's not a good comparison.