I have a 2001 rancher 4x4 ES and it's been a really good quad. No problems out of it except the frozen choke cable that was common with the early ranchers. It's been pretty much bulletproof and I don't see how you can go wrong with one.
If I were buying a quad today I would get either a rubicon or a 500 foreman, probably the rubicon due to it's hydrostatic transmission. Whatever I got it would be a honda, no other brand of four wheeler for me. I'd pick one of the larger quads over the rancher because sometimes the rancher just doesn't have enough power to suit me. I'm a big guy and it's just more pleasant riding a quad that you don't have to constantly shift in order to keep it in the powerband. The Rancher's not really underpowered, but the bigger bikes don't make you downshift as much to keep things moving, they're a little more pleasant to operate.
I will not own a four wheeler without four wheel drive. A 2wd quad is pretty much a useless invention to me. The 4x4 isn't much more expensive, and it increases it's utility ten fold. The first time you do that two mile walk out because you got stuck you'll wish you had the 4x4. A winch is a good investment, mine's saved me a couple of times, even with 4x4.
They're changing the rancher for the 2007 model year. It's rumoured to have a selectable 2wd/4wd and an independant rear suspension. It should be out in a couple of months, I'd hold off buying one right now until the new ones appear, you might like them better.