I would vote for a mini-van vs. an SUV. With 6 kids, I have really had ALL types of vehicles, but my favorite for easy with kids was the mini-van. The biggest issue for us was always swinging the door open (versus a slider door) and ramming it into a neighboring vehicle. I have also had a door swing shut on a kid and even myself when it is windy out.
I have had 3 mini-vans over the years - a Toyota Sienna, a Pontiac Montana, and a Dodge Grand Caravan. I personally liked the Sienna the best (although we had the Montana the longest). I don't think that Pontiac makes the Montana anymore so that probably isn't an issue (unless you find an older used one).
If it were me, I would look for a used mini-van with dual auto sliding doors, but be willing to give up any other amenities to help with cost. I would stay away from a car as it will become less useful the older the kids get - even if car seats fit (we have a car as well and would never drive any distance with 3 teens in the back seat - what a nightmare!). I would also only buy something with 3rd row seating and captains chairs in the 2nd row (this is a blessing in a million ways, trust me).
If you can afford the extra charge, consider mini-vans with AWD. We had that in the Montana and LOVED it in the wintertime!
Good luck!