But there are a few to choose from. There is the R.A.T. 3, 5, 7, and 9. Does anyone have experience or know what the major differences between them are?
A buddy of mine still uses his RAT 3, although why, I honestly don't know. Although it looks freakishly cool, it's not that comfortable for my palm. I would suggest you visit a store and just grab one to see how it feels. On the hardware side of things, it's more than decent and it is capable.
Well, I was going to get a RAT MMO 7, but decided against it after reading some reviews. Most of the reviews, initially, are great; they're pretty good mice, look cool, and are generally comfortable. Lots of buttons, as well. However, the downside of the mice is that they only last a few months, or so, before beginning to break down, and possibly only 6 months before completely becoming unuseable. Now, obviously, that isn't going to be every RAT mouse. They simply have a QC issue - it is more of a gamble, compared to buying something like a Logitech g600 (great mouse, by the way; I got it instead of Cyborg RAT 7). Buy at your own risk.
My wife uses a RAT5 and it's the ideal mouse for her. I don't think they're that comfortable myself. Everyone his/her own taste in mice, that's normal. However, Saitek makes good stuff (I use their flightsticks, don't want anything else), the hardware quality is very good. My wife also uses the Cyborg keyboards, they are good quality too, although I don't like the keystrokes that well personally, but they are better than most generic membrane keyboards.
Try it out and see for yourself. There are return policies for a reason.