Particularly in the price range you're looking at, condition is more important than brand or mileage or age (at least within reason). Look carefully to ensure that proper maintenance has been performed, particularly with regards to keeping up with caulking and seals around the roof, etc. Water damage can be costly and/or time-consuming to repair, and is very often more extensive than it would appear from the outside.
A number of people here have had good results with purchasing an ex-rental RV from CruiseAmerica or similar large rental agencies. They do a very thorough job of reconditioning their used motorhomes before selling them, and the result is something that will give good, reliable service. It's an option well worth considering.
