For me it's GTR2, solid base made so much better with all the mods (although sifting the bad from the good could be a pain), I spent ages tweaking Ai files to make countless mod tracks perfect challenges for me, and I can't forget the first time I blew up the engine in my favourite Lambo with a dodgy downshift, also can't forget ogling the back end of a F550 as I followed it rather than overtake. I dread to think what the tally of my hours were in that game, thousands upon thousands!!
Honourable mentions:
Sports Car GT was the first game I played with a wheel (early logitech) and was awesome, a real step up from using a joystick in the Geoff Crammond games and the point I realised tin tops were better and more fun than open wheelers!
GP500 by Microprose, brilliant bike sim.
GT3, perfect blend of awesome visuals and physics (PC games were visually not as good as console games, thank god that gap has been closed)
Honourable mentions:
Sports Car GT was the first game I played with a wheel (early logitech) and was awesome, a real step up from using a joystick in the Geoff Crammond games and the point I realised tin tops were better and more fun than open wheelers!
GP500 by Microprose, brilliant bike sim.
GT3, perfect blend of awesome visuals and physics (PC games were visually not as good as console games, thank god that gap has been closed)