Re: mnt bike vs cruiser...
Having had a rack mount on both I would probably go with the Cruiser myself.
They are generally stronger and heavier built (always good when adding a motor) and have a nicer riding position. The only proviso I would make to that is a dual suspension mountain bike - probably the most ideal machine of them all..
hope that helped
"....Look, no pedals... *thud*..." The mating call of the motorized-biker.
"RetroEagle" - 32cc Two-Stroke, Piped. 35mph on #13 gear. Reversed stem with springer fork.