but the MPV and car would be nicer to drive (presumably)
not neccesarily – depends on what you like but most vans are very comfortable these days.
The two big differences will be…
Hire vans are usually cheaper like for like / size for size and the main reason for that is an element of the cost is insurance and a factor in the insurance is the number of passengers you can potentially harm/kill so with a car or MPV you’re paying to insure empty seats if you’ve only got one passenger
A hire van will look like you hired it – it’ll be liveried with the company’s details.
Theres also to less to worry about keeping clean with a bike in a hire van – hire co’s can be a bit fussy about clean interiors in return where as so long as you’ve not left rubbish in their they’re less bothered about the back of a van