I rented a 15 passenger van from Dewey ford and thought it was great. Very clean, was ready when I was scheduled to pick up, no hidden charges, pretty smooth process.
My wife tried a small place on the southside, I think A to Z, but not sure, for a van for a bachelorette party, and it was horrible. The van was dirty, and when she went to pick it up the battery was dead. They had to jump it while she waited and they told her to just let it run a while and it would start fine.
I'd go with the dealership.