Minivan!!
Oh alright. If you don't want a minivan, personally, I would consider a Suburu wagon. All-wheel drive and some room for equipment. Gas prices are going to keep climbing. I would factor that. If you want a smaller car, the VW Golf W32 or GTi would be nice. High speed-Mitsu Evo. All would be good here in the midwest. All can be had for under 30k.
I wish we had some real diesel cars to choose from. I would buy a C-clas MB 4matic diesel wagon in a flash. The US sucks for getting the goods.
Whoops-missed the "used" part. Then consider used legacy wag, MB 4matic E-class, BMW 325iX. All can be had for under 20k. But, by the time you factor in financing incentives, you might be tempted to buy new. Depends on your budget.
the right car