Originally Posted by rtsukijima
You'll find floor plan to be an important feature as well.
Great advice above! I just completed a 3000 mile-ish trip in my 97 Dodge PW. It has a 318 v8 and it averaged 14-16 MPG.
If you have a family (even if your kids are small), I would consider floor plan (space) to be the most important factor. Especially important if you plan on taking extended trips (more than a weekend).
Hope this helps.