Vaughn really hit the nail on the head with his first post. How many people? For shorter trips, or living in for a long period of time? Does it need to be dual use, or can it be dedicated for camping? What sort of amenities do you want? Do you want/need 4wd and clearance regularly? It is important to be honest with yourself about what your needs are.

My wife and I used a Eurovan (no pop-top) for years, and it was great for our needs at the time. It could carry 5 people with whitewater kayaks on top for day trips, was decent for weekend camping. Now we have a Sprinter that I outfitted myself, and we love it, especially now that we are retired and take trips that last for weeks or a month+.