Both have videos featuring the new Ferrari 458 (that's replacing the 430) and its not even for sale yet Here's videos from both games: Forza http://forzamotorsport.net/en-us/media/videos/default.htm?mediaid=2322#/video/2322/ GT 5 http://ps3.ign.com/dor/objects/857126/gran-turismo-5/videos/granturismo_trl_458italia_92209.html Gotta say, GT's light reflection looks amazing.
GT5 looks so much better than forza. Then again, it should. The game has been in development for ever and it probably will be for another 5 years lol. Can't wait for forza to come out though. I'm actually excited about a freaking racing game.
http://www.youtube.com/watch?v=3lO4KQ74r3g&feature=player_embedded Warning, this is not work safe... you might wet your pants!