A mouse is not something one should be changing with any regularity. Get one that will last and become accustomed to it until it is an extension of your arm. I had used an intellimouse optical for at least five years (and there was nothing wrong with it in the end, I just wanted to move on) before trying a Razer (bad idea) which was quickly replaced by the G5 I've been on for about five years.
Anyways the feel is the big thing. The G5 is infinitely more comfortable than cheapo plastic mice. The one-touch DPI setting is useful for sniping or other instances requiring finesse (like graphic design). Customizable weights is just gravy (I tried the G5 weightless for a while but I prefer a mouse with heft).