Razer Naga + Logitech G15 FTW imho.
I have heard that the steelseries WoW mouse was plagued initially by a lot of faults and build quality was bad. Google the initial reviews out there. Not very favorable so just be forewarned. This may well be a newer iteration but I bought my naga after comparing the two at a shop. The naga just feels better built and more ergonomic, and ... having another razer mouse for FPS, to me they have proven themselves as pretty good mice makers, good enough for me at any rate.
The G15, well, I've had this for YEARS, it's taken quite a hammering (some games are more demanding than others!) and works as new. Tough, reliable, flexible, programmable. Possibly the only thing I'd replace it for would be another G15.