I'm not voting because I didn't try them all! But I'll share what I'm thinking about them!
NFS Shift: +
It's a good game, after trying the demo. And people say the full version feels better! I'm just not thinking about buying this one because I can't run it safely. (the demo crashed to desktop 9 out of 10 times for me)
My processor is under the requiements so I think it's not really the fault of the game but my PC is just too old.
Race On: +
Race 07, it's a great game. The 2 new cars in the demo were great, and this game has a Lada! So it can be my favourite!
Forza 3: + (?)
Seems to be an awesome game but I couldn't try it yet!
Race Pro: -
I couldn't try it yet but I imagine it's something similar to the PC version with less people in multi and worse grahics (yes, I think it's worse, it's just not right somehow)
F1 2009: -
I can tell from the videos that I don't like it. Maybe on my phone, while I'm travelling I would like something like that, but I usually prefer to play games like Quadrapop there!
Dirt 2: + (??)
Two "?"-s this time. I didn't try the demo yet but it seems good. This is for the 1st one.
The second one is because it's a rally game so I can get bored with it soon if they didn't have some great idea that they put in the game to avoid that
Supercar challenge: + (?)
Didn't try it yet but it seems good. The sounds are especially awesome in that game!