At my hunt camp we run Big Bears, Suzukis and a Grizzly 660. The 660 gets bogged down and drowned out where the smaller Big Bears just walk through. The Suzuki has broke down many times.
I would suggest a 400cc class with 500cc as the top range and to avoid a the rubber belt drives if you plan on going through much water. Honda or Yamaha are all I would consider. Make sure you buy a winch and aftermarket tires are also a good upgrade.