If you are transporting babies or the wheelchair-bound: Minivan, because of the sliding doors, lower distance to the ground and the ability to pull out one of the middle seats to accommodate three carseats.
If you have to drive in bad conditions (rural and snowy or muddy): SUV (true SUV, not crossover), because of the raised platform and AWD (yeah, you can get a Sienna with AWD but that is an expensive option and you're unlikely to find one used)
If you have to haul things, like a boat or horse trailer: SUV (again, real one on a truck platform).
If you drive and park in crowded city streets: Then you really shouldn't be driving EITHER one of these vehicles, damn you, but Minivan (or crossover SUV) wins... the more nimble car platform, lower weight, and lower braking distance, of a minivan or crossover is more maneuverable for the average driver. Now, if you have the skills to pass the test for a CDL today, ignore me.
Mileage: Likely a hybrid minivan, though you're not really winning with either choice.
Maintenance: Tricky, but minivans usually have lower ones than true SUVs plus true SUVs have costlier tires.