Wow Heatshock, I could not have said it better.
I would think ABS would be better for something you didn't plan on painting, kind of like a Stormtrooper suit.
I have been building suit's out of HIPS since early 2005 and have no problem with paint sticking.
You have to prep it with Primer and I have always use Krylon Fusion paint (which is made for painting plastic).
Plus like Heatshock said, you have to glue, bondo and sand the seams.