They both look impressive but I'm going to get Forza 3. The paint options for that should be awesome. Also theres a huge part of me that thinks NFS will be aimed at the mainstream rather than more hardcore gamers.
Yeah, I'm a GT fanboy (look at my avatar) but I'm actually looking forward to both these games. 400 cars and the inclusion of Nurburgring and Le Mans makes Forza 3 seem like a clear winner to me (although I'm sure Shift will be really good too).
I've loved the NFS franchise (minus the last 2) and I've loved the Forza franchise.
Unfortunatly for SHIFT it lacks too many of the features needed to compare to other true sims, mainly 400 cars and 100 tracks.
I like to tune cars and I like to race them. Odds are, I WILL use and tune at least 50 or 60 of Forza 3's cars which is nearly the entire car count for SHIFT.
I am eagerly counting the seconds until Forza 3. 2 was my first ever sim racer, and it was freaking great. Never before had I played a racer without trying to crash people (well, I did that a little too, but still)! The tuning and customizing was the best, though, because I never thought I could get so excited about shaving seconds off of my lap time. For me, GT for PSP has 800 cars, so I think it's a bit pathetic that NFSS has like 65. That's a bit lazy. And yes, I use almost all of the cars. You need certain cars for a certain track because of how they can be tuned. I highly doubt NFSS can make me enjoy the meager amount of content they're trying to fill their game with. Money-grabbing, really. It'll sell well too, which is really a shame. Hopefully NFS will be dead by next iteration, especially if they start charging real money for retarded useless crap like in Carbon. Goodbye NFS, say hello to the future: GT5 and FM3.