The 360 controller allows for XY axis grid vision (You cannot actually see it, but moreso feel it when holding the controller). This is perfect for hand, eye coordination.
The PS3's analog sticks are side by side, which is not good for hand eye coordination. If a person who was good on the ps3 at shooters, he'd be amazing on the 360 with the freedom the controller gives on Racers and Shooters.
The 360 controller can easily be replaced if you want to use a fighter. I bought an S-controller when I wanted to play Soul Calibur 2, back when I bought the first god forsaken Xbox. I like the PS2 Layout for the controller, it's heavier and more sturdy for fighters, while the PS3's controller is lighter and the back R2 and L2 buttons are rather annoying. The PS2 controller fit better in your hand. I find that the PS3 controller is rather redundant.