I too have a decent PC, well, it was 2 years ago when I built it but it still performs well in most games when I overclock it. Also have an Xbox 360 and easy access to a PS3.
And the one I play and enjoy the most is the Xbox, it's more of a social console, relatively cheap, has very good graphics for the price and only costs about £25 a year for XBL. Overall it's just an easier and more enjoyable experience.
PC gaming is also good, but it lacks the social feel for me and a PC will need upgrading every couple of years to play the most recent games at a good quality. Which whilst that is something that I can afford to do, it's something that I don't do as I don't use the PC often enough to justify spending a lot of money upgrading it.
As to the PS3, it's more of a media centre than anything else to me. Fair enough it plays games, but there is still a lack of quality PS3 games. And any multi-platform games I get for the Xbox as online seems more reliable and of a better quality. The blu-ray player is the main feature of a PS3 for me.