I'd vote minivan, but it is nice to have smaller, since most of the time a vehicle is moving air. Probably the Grand Caravan, get something cheap, then beat it to death--kids are kinda rough on things.
Space is good. My A4 was lousy with rear facing seats--and we are not that tall. I don't think it will take three booster seats across the back; given the small back seat I think my kids skate by just fine w/o now--but they sorta still need them. Kid seats are not small.
We thought about Mazada5 but went Camry in the end. The amount of trunk space is amazing; we somehow managed to get one of the last stickshifts also. I think the Camry might actually hold more in the trunk than my wagon, assuming the seats are up. Certainly larger. Yeah, three kids is the max, as is 5 people total; but we also never wanted to deal with broken electric sliding doors, which seems to be a common complaint, or a bad trans (maybe Dodge has fixed that now?).
We've managed with a Civic in the past, did the Jetta for a while, but are pretty content right now with the Camry, with just two kids. Three and we'd probably have a minivan, only because of trunk space issues I'm guessing.