sad to say i dont have a fave on pc... the closest the pc has come to a decent race sim is shift 2 but that needs mods to get it to handle as a real car does.
gt4 on ps2 tears holes in gt5 and forza has always been a bit second rate as its seriously limited by the hardware... forza 2 was probably the best version of the series because it pushed the hardware with no compromise, i cant say the same for the next iterations where they removed some visuals to get the frame rate up then put them back in its photo mode. only to claim that the extra gfx were in game footage(well they were if you wernt actualy playing)... but still thats sneaky...
over all there is little that compares with gt4 on any platform which is a real shame...
gt5 turned into a bad joke... they seem to have stripped out the physics and made every car handle virtualy exactly the same... there is no difference in handling between a MR and FR drive cars and FF cars drive like they are 4x4's, after so long in development it was a real shame that the game didnt do its forerunners justice...