I agree with Stoobidbot, that the Grizzly may be tougher, and if you want to ride rough, it would be the better choice. I would also like to add that the Rancher is not incapable of being a decent trail rig. A freind of mine has an '04 Rancher 350ES, and he rode the hell out of it for the next 4 years, mudding, trail riding, jumping, and just beating the hell out of it in general. Granted, it is now damaged beyond conventional repair, but it was flat out abused on a weekly basis for over 4 years. If he would have just kept all four wheels on the ground, I think it would still be fine. It still runs and rides, but the swingarm is loose and it will take some refabrication of the mounts to properly fix it. Bottom line, considering the abuse and lack of maintenence, I thought it held up pretty well.
Yours truly, sincerelly, love always, Josh aka The DirtDemon.