One thing to consider in gaming mice is the ergonomics. My current gaming mouse is a Razer Boomslang, selected because the low profile and long left and right buttons encourage me to lay my hand flat on the mouse and use it by moving from the elbow. My previous mouse, a Logitech Cordless MX500, sits gathering dust, because its higher profile causes me to grip it between thumb and ring finger and move it with my wrist. This causes shooting pains up my arm after a relatively short while, especially in games that have a lot of “right-click for mouselook” like World of Warcraft.
I flirted briefly with trackballs, and found them to be insufficiently responsive for gaming, and no better ergonomically for me – I just transferred to overusing my thumb.