Isnt it like.. a matter of view/opinion?
I own Gran turismo 5:prolouge and ive played with plenty of friends on their xbox with Forza.
IN MY OPINION i feel gran turismo is way more... ''car realistic simulated'' but thats just me lol.. Forza is an amazing game too so dont get me wrong. I AM A PS3 FANBOY. Might want to think about that too XD, But in my opinion i perfer Gran turismo over Forza. And i actually find everything on GT better then F (Speaking : Graphics, Layout, Cars, Simulator etc.. )
Remmeber i own Gran turismo 5:prolouge, I only tried forza several times but i dont own it, and im a fanboy.
(If this was a thread like Halo vs MGS4, id be going like GTFO MGS OWNS. But hey! fanboys can be civil sometimes XD).
And GT5 will probably > all racing games. IMO!