IF I can only pick one and if I even get one...not sure yet, I'll get GT5.  It's just such a classic, super high quality, and I have a GT racing wheel and chair to boot.  But we'll see--I haven't been that excited for racing games this generation.  Mainly just a  music game and JRPG fan now-a-days.

I like the thought of 1000 cars. I will never be able to use them all so GT5 it is! :D

Easy

From a racing fan perspective = Forza 3

From a gaming fan perspective = Forza 3

Gran Turismo series has been crap since 2001. Any real racing fan will tell you that.

GT5 because it has more content (like twice the cars or some shit) and although I do like racing games, GT5 will take long enough to beat..I don't have time for 2.

lol but the fact is, that it hasnt been crap since 2001.

NONE because I suck at racing games.

gt5

I never play racing games, besides Burnout Paradise.....

But im buying 2 copies of GT5 just because of Waron.

ModNation Racer

Because I have absolutely zero interest in realistic racers.

Forza 3 for me, simply because i find the PS3 controller's analog stick at an awkward position, and not enough resistance to play racing games, well that and because Forza 3 to me is raising the bar on what to expect from a real driving sim. GT 5: Prologue and GT: PSP didn't address the issues i've always had in GT games, which were perfect AI, lacking sense of speed (i'll be going 100mph on my speedometer, but it looks & feels like 50mph), and damage collision.