You cannot go wrong with a Honda. My grandpa has a early 90's FourTrax that has been beat to p***. He use's it on his farm/ranch and I would hate to guess how many hours/miles are on it. He has had no problems with it at all. My uncle had a Kawasaki Prairie and put around 6000 hard miles on it and had no problems with it. Like others have said, check it over really well. Some may look nice but have not been properly maintained.
Check out the 300-400 Kawasakis and Hondas. The manual shift models of those brans are bulletproof. My 95 Kaw 400 is still running as good as a new one.