Hitch racks are great if you can't actually put the bikes inside (my voyager is a cargo van, not a family van) With a roof rach you may need a step ladder which is not convenient.

You can't beat a van for capacity though - at one time I have had 12 tandems mounted to mine. 8 on top and 4 inside. Boy did I ever get a lot of points and stares on the way to the tandem demo. One guy asks me at the light - how many of those do you ride? I said, one at a time...