Floorplan RULES. I'm pretty sure both options would be a quiet, comfortable drive and ride.
BUT!!! Be sure the carrying and towing capacities of any ProMaster-based coach will meet your needs. The Sprinter-based units have considerably more of both.
For that reason, a used Chevy-or-Ford based unit might just satisfy your needs, leave capacity to grow into. Yes, at a decrease in fuel economy. You have loads of options at the price of either of the ones you're considering new.
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB