What are you using now and what would you want from a perfect mouse?
Wider?
Longer?
Taller?
At home I use a Logitech G700S.
At work I have a simple Roccat Kova [+].
I also own a CoolerMaster Storm Inferno, which I only stopped using because the G700S has more buttons!
Another to consider is the Roccat Kone.
All these were a fantastic fit for my XXXL glove sized hands and I'd highly recommend them!!
I have used a Saitek Cyborg R.A.T 9 and while it does fit fairly well, the other features and naff build quality killed it.
I've used several Razer mice and while they're nice, long, well-fitting mice, I again found their cheap feel and general features turned me right off.
I was right on the verge of buying the Steelseries WoW mouse - The earlier edition with the sixteen buttons. That was a very good mouse... but it was flippin' pricey, I'm not into WoW and it just looked silly!