A few things to think about:
What are the minimum number of seats you want/need?
What are the differences in potential maintenance and repair costs among similar models?
What can you afford?
Which gets the best mileage?
What are features you must have – tinted windows, rear air, side door opening on both sides, etc.
We had a 12 seat Ford van. We were told that the E150s were cheaper to maintain, less likely to need more costly repairs than the E350.
We were thinking of downsizing but wanted at least 8 seat belts, which led us to an Astro. We then found out that Astros guzzle about as much gas as full size van. (We would still have to rent something bigger than an Astro for family trips, so not much savings there.)
Just some ideas to get you started.
Oh, and then, if all else is equal, aesthetics.
Hatzlacha and may you use it in good health, for good things.