Most SUVs and MPVs (more correct term for AUVs of today

) will not fit grown people at the back no matter how big the car is, cramped 3rd rows are usually the norm. I'll cite our Trooper as an example. Even being a proper midsize SUV that is designed to carry people at the 3rd row, if you don't want your head pushing against the ceiling, you'd have to be around 5"6 and below and then there's the issue of legroom. There was this once when I rode in the 3rd row of a first generation Expedition. The ride was comfortable all right, but the headroom is certainly lacking, and that is a full size SUV.
In order to comfortably fit six full size adults, it'll have to be in a spacious 2-2-2 configuration, and the only SUVs I can think of right now that can do that is the Suburban and the Expedition EL.

Otherwise, it'll have to be a van.