I have used a full size Chevy PU, Chevy s-10, Extended Astro van, Dodge Dakota and now a Scion Xb.
I bought the Xb for the novelty/marketing factor when I relocated and basically had to start over. It is as you mentioned, a rolling billboard.
Utility and fuel mileage were also factors, but on down the line from the novelty.
When I say novelty, I have an image of the fully lettered truck (not really a truck, but what else do you call it?) on my cards, web site and brochures.
I don't get many calls (but I do get some) directly from the truck, but I do get recognition.
"Oh, your the guy that drives the little box..." type responses when meeting people, etc.
I am fully satisfied with the lettering/marketing aspect as well as the usability factor of the vehicle. 30 mpg ain't too shabby either. Also, Fully loaded the price was less than $16,000 including roof racks and lettering.
It is much easier to work out of than the van, full size trucks, etc. The only thing that came close was my S-10 pickup with a topper that covered my tools, etc.
My only real complaint with the Xb is my choice of ladders has to go on top out in the rain and freeway muck, but I use the largest convertible ladder I could find.
If I used anything shorter, I would have it inside since there is plenty of room.
If you want to see it, go to my web site.
Mr. Inspector.Net - Mr Inspector - Allen Texas - Allen