Welcome!
First, it has to be appealing to both of you, floor plan, kitchen etc.
Second, I look at condition and maintenance. Check for records and ask the owner a ton of questions if you buy private party. From a dealer, same questions. In both cases, I would pony up the bucks and get it professionally inspected.
Third, do your research on the net for the models you have an interest in for common problems and other information.
Fourth, take it for a long test drive. Preferably with all types of roads and check how the rig feels to you.
Its a large investment,take your time and don't let yourself be rushed into a decision.