I think this totally depends on your price range, where you'll be driving and what you'd like to do with the car. Vans are very useful, tend to guzzle less feul while remaining roomy. My family has had three dogs in our van and they were always comfortable. You can take out seats either in the middle of the van, back, or both, in order to create an even nicer place for your dogs. I think you also get more for your money when buying a van, as opposed to an SUV.
SUV's are pretty in style, though. There are many new SUV's that are nice and medium sized, even a couple that are hybrids (if you are concerned about gas prices)... Toyota just came out with a new hybrid SUV. Like I said before though, if you're not planning on off-roading, aren't too concered about being practical rather than following trends, and want something very nice for the dogs, I'd reccommend a van... either a Dodge/Chrystler or a Honda. They are great vehicles.