I suggest you choose your system based on preferences and which games you wish to run.
Personally, I stiull recommend the PC. There are tons of fantastic games out there, real life sims that are ultra competitive, unforgiving, and realistic. Games such as Rfactor
http://rfactor.net/ and GTR 2
http://gtr-game.10tacle.com/index.php?id=246&L=1 just as examples. Mix in quality wheels such as the new Logitech G25
http://forums.beyond.ca/showthread/t-130246.html and add the video candy of three monitor display offered by Magtrox Thiplehead
http://www.matrox.com/graphics/offhome/th2go/home.cfm, then you're talkoing about realistic, fantastic fun.
Personally, I go in the direction of my PC with the fun goodies.
The graphics are unmatched, the gameplay is realistic and as tough as it gets, and there are tons of leagues and races to be found 24/7.
Oh, and by the way, can you load additional tracks, or paint your car as you like? I can.