I've never been huge on the Xbox 360 controller. I love the larger number of buttons and the sturdier sticks, but it's a big honkin' piece of plastic and you can't deny it. On the other hand... Sony's been using basically the exact same controller since the PS1, and you can't deny that either.
Of the two, the main thing is that the 360 controller has TOO many buttons, and even with my large hands I have to stretch to hit one of the weird half-hidden buttons on the other side. I'm used to the PS controller because I've used it for years. I imagine there's a perfect controller that's halfway between the two, but it'll never be.