With this generation of consoles there is only so much that can be done in the graphics department. There ARE limits but both GT and Forza have done an excellent job of graphically representing virtual driving/racing on their respective platforms. It just looks like Forza 4 is more "consistent" graphically across the board. I sure wouldn't base my purchase or game time on the graphical capabilities of either. Couldn't say the same for F1 2011 for an example. With that game the developers "failed" to find the PS3 horsepower to provide the same experience as the other platforms.
To me this VS discussion comes down to fun factor! Many of us here on GTPlanet have both a PS3 and Xbox and own both GT and Forza. I myself switch between these tools to play my software of interest. We can nitpick till we are blue in the face but the end result will come down what disk we will be poping in our consoles. My preference is a "racing" experience. I have no interest in AutoVista or collecting paint chips, museum cards, racing suites, or 10 variations of the same car, etc.. I want a racing sim to represent "racing" virtually.
My Top Ten virtual racing gaming decision factors:
1) Must excel graphically in representing a driving or racing experience.
Both systems have this covered.
2) Must provide sufficient RL racing environments - real tracks.
Both systems have this covered but edge to Forza.
3) Must provide a good selection of road and racing vehicles.
Both systems have this covered.
4) Must excel at replicating the sound or the IRL cars.
Forza
5) Must excel at providing the driving "feel" though a gaming controller.
Both systems have this covered.
6) Must provide a challenging AI for offline competition.
Forza
7) Must provide a mechanism or features to customize and personalize our virtual cars.
Forza
8) Must graphically depict vehicle damage as best as possible.
Forza
9) Must be as convincing as possible in replicating IRL consequences of contacting barriers and other cars.
Forza
10) Must offer a way to compare or measure results with other gamers.
Forza
11) Must offer a cockpit racing view.
Forza, GT partially.
Ok, top eleven. Of course this is my opinion based on my preferences. Like anything, as time passes most things in life get improved upon. For me, in the fall of 2011, it's Forza 4 that will excel at providing my top 11. GT6 may leapfrog Forza and if so I will switch software as I have no allegiance to any platform.
OP was FM vs GT and posted in a FORZA FORUM. Forza enthusiasts of coarse could be biased to some extent just as GT fans. But to me this was posted in this FORZA forum for discussion between primarily FORZA fans while waiting for the next gen of Forza. Sorry for the long "personal opinion" post.