Forza isn't comparable to Gran Turismo? At all?
I've only played the Demo of Saints Row, but it seems like it's better than GTA. Obviously the graphics and animation are better. The action (especially aiming is much better), and the missisons seem similar. As far as story goes, it doesn't really matter since GTA has crap stories anyway, and the games are repetitive as hell and get old way way before you get anywhere near the end.
As far as the system goes, I haven't had any issues with it. Granted I don't play it 10 hours a day like some people, and I know how to take care of my stuff and not be stupid with it by putting it on shag carpet or something. I don't think the PS3 will be that much (if any) better really, and it costs a lot more...which depending on if you're wanting blu-ray may or may not be worth it. I plan on getting one, but I get everything...and plan to sell a few PS3s on ebay to pay for the one I keep.
If you can't decide, just pick up the 360 at wal-mart, rent some games, and see what you think. If you don't like it, you have 90 days to return it.