Hi There,
I think that most would agree that it depends on the skill of the driver.

If you expect a few knocks and bangs (from a younger driver), then a good quality, exterior gloss, brush paint will be great, then small touch ups can be done.
If your pilot is a little older, and more co-ordinated, then a couple of coats of car spray is fine.
The thing to consider is that Gloss paint is easier to re-touch and quite in-expensive, and 'Automotive' paint is the opposite, but gives a better finish.
In either case, it's down to the preperation of the surface.
MDF is already very smooth, so a good quality sealer (as described by Richard in the build manual) and then careful prep of the surface is needed, to acheive a quality finish.
At the end of the day, these are designed for children (although we all forget this), and you should expect a few knocks in the first few months (or 12 in my grandsons case).
This subject has had coverage in the past, and is on page 2 of the 'General Discusion' section.
Keep Busy,
Regards,
Mark.