We have used Tiffany, and love them. The first time we had the van, due to babystrollers, carseats, etc. It wasn't as comfortable as the towncar, but still nice.
When you add the fact that they give you a grocery stop, it helps add to the savings. When you figure that water is $2.50/bottle, at the parks. For a family of 4 @ 2 bottles/day, that is $20.00/day, just for water. For our 8 day stay, I saved about $145 in water alone, by using the grocery stop.