Rick,
If you want the best of the best, I suggest checking out the Sportchassis M2 Freightliner. It is a MDT that will tow any and every 5th wheel out there. Here is their link...
www.sportchassis.com
There are some down falls to having a MDT; parking, no 4x4, and cannot take them through the carwash. On the other hand, they will be within every spec possible with any fifth wheel you buy.
If the M2 is more truck than you are looking for, I suggest sticking with any of the 1 ton diesels. The 2500HD can tow and haul a Montana within every spec on the truck, but it probably will not happen if one is going full time. Having the extra payload capacity of a 1 ton will be beneficial as you load up your coach... Happy shopping.
PS~ here are a few other links for MDT's out there
www.haulerking.com Chevy Kodiak 4500's
www.neelycoble.com Freightliner M2's