First-person shooter fans generally prefer the controls of a PC, using a mouse to aim and the keyboard to move around. You get more buttons for access to hotkeys and you can fire while looking around more easily. Console controllers are a little more awkward for such purposes and take more getting used to. Some people don't think that has to be the case, however.
A fellow who goes by the name of "Foo Foo" modified an Xbox 360 controller to be more FPS friendly, moving the buttons to the underside of the controller, allowing you to hit buttons with essentially all of your fingers. This lets you keep your thumb on the thumbsticks at all times while hitting all of the buttons, giving you fewer delays in your precious fragging. Unfortunately for you, it's not for sale, so it's time to start figuring out how to dismantle controllers if you want the same thing. Or just buy these similar controllers.