Personally speaking. I would always fit the smallest wheel possible to clear the brake discs for three reasons.
1. Higher profile equals a more compliant and comfortable ride.
2. 16" Tyres are generally MUCH cheaper than their 17" or especially 18" counterparts.
3. FAR better and cheaper availability of winter tyres.
There are more reasons that are, to me, completely personal, one is that I think that tyres below 50% profile have no place on Britain's roads, particularly on a "family" MPV. I think they are utterly "naff" and can only detract from the comfort and usability of the vehicle.
I once went to look at a Mk3 Mondeo 2.0TDCi Ghia X which some clown had fitted with ST alloys. I test drove it and liked the car, except for the wheels, which destroyed the ride, tramlined badly, and produced the worst road noise I have ever heard. In comparison to my Brother in Laws similar car with standard wheels it was appalling! I tried to convince the salesman to give me standard steel wheels in place of the, frankly, hideous, ST wheels, but he wouldn't. He insisted that they were a "selling point" . He didn't get a sale that day! In retrospect, I should have bought the car and unloaded the crap alloys on ebay. I could have bought all four steels and tyres for the cost of ONE ST tyre!
2008 2.0 TDCi Zetec