I have had great service out of goodyear mudrunners as they provide great traction in all terrain and light steering.Mud bugs are highly rated as well for an all terrain tire.I just bought a new rubicon and am trying gators on it as they are supposed to be a very good all terrain tire as well but at a more reasonable price.As to sizes I generally go one inch larger in diameter and one or two inches wider than the machine came with.If you go too big you will change your overall gearing too much and it will feel as if your machine has lost a lot of power.