Little kids get bigger every day. If you’re uncertain, I’d just keep the Suburban a bit longer if you aren’t putting that many miles on it. Of course, that means you’re probably putting miles on the Saab instead, which is OK, but it commits you to keeping it unless you want to add those miles to the Suburban or your work van, neither very efficient (not that the Saab is super efficient, either). Anyhow, five is an awkward size for a family vehicle. Now, when they’re small, you might be able to seat them three across in your Saab’s back seat, but in the future that won’t work. When I was young six of us sat in a full size car, but those cars were designed for it. The back seats of even big cars seem designed for two people, with a third person having to sit on a hump in between. Kind of stupid given the available width. I guess they expect everyone with more than two kids to get something bigger than they really need.
So, minivan or three row SUV? Minivans are typically wider, and have more cargo space with their lower floors. The Honda Odyasey and Toyota Sienna are easily the best. The Chryslers seem OK, but their reliability is awful. The Nissan Quest is smaller and less clever in its packaging, and the Kia Sedona is ancient. The smallest possibility is the Mazda5, but that would only work for the few years your kids are small, as the third row seats are strictly for smaller kids. Likewise compact crossovers that offer a third row. Just don’t bother unless you want to have to buy a replacement in a few years.
Mid-sized (actually pretty big) crossovers like the Honda Pilot, Toyota Highlander, and Mazda CX9 are all quite nice and offer ample room. Consumer Reports has given a glowing reccomendation to the Hyundai Santa Fe in this class (not to be confused with the smaller Santa Fe Sport.) It does seem a big improvement over the model it replaced a year ago. I especially like the Mazda, which offers a surprisingly luxurious interior that could come out of a Lexus. Consumer Reports also likes it. Access to the third rows is always worse on crossovers than on minivans with sliding doors, but the young can get back there easily enough. The crossovers do have the advantage of being readily available with awd. Of minivans, the Sienna is available with awd, though ground clearance is limited so it’s just for road use. The Odyssey is strictly fwd. With proper winter tires there are few places you could go in one but not the other, though the availability of awd is nice. Of course, all the crossovers have it available. If you find yourself filling up your Suburban with stuff, these will all feel small to you. The minivans are roomier.
If it didn’t have the annoying reliability problems of current Fords, I’d also be suggesting the Ford Flex, a more carlike solution. It’s one of the few vehicles that can plausibly carry three in its second row, leaving the rest for cargo (or more people, if you use the third row. I think my affection for it springs from it resembling the big station wagons of my childhood, the sort you could carry a 4x8 piece of plywood in back lying flat with the tailgate closed. The Flex is a bit taller and has awd available, but my dad would have felt right at home behind the steering wheel. You sit at a nice height in the Flex. You just slide right in, no climbing, no dropping. If you have very small kids, loading child seats would be easy.