My first recommendation is to try for a quad that is shaft driven. Most are now days, but I would stay away from any chain driven ATV. Determine what engince size can fit the bill for the work you will be doing. So, how tall and heavy you are, what you will be carrying and or towing will likely narrow down the choices a bit. For general riding and light hauling a 250cc quad will do fine. However, if you will be on it each day, roung terraine, carrying a couple to several hundred pounds, I would look for a quad that is atleast 350cc and up.
My choices would be Yamaha Big Bear 2X4 or 4X4, Any number of Honda's fourtrax, rancher, foreman, etc... Suzuki quadrunner ( think that is the model) 500cc, Kawasaki Bayou 300, or prairie models, Artic Cat 250 4X4, 300, or 400cc.
A brand new Artic Cat 250cc can be had for around $3700.00. Good luck.
markc