Personally, I would rather buy a Chev/Ford chassis due to the broader network of dealers. The Ford E450 will offer you a GVWR of 14,500# and Chevy just a tad less but the Chev will offer a little better ride and little more foot room for the passenger. I had to spend some money to upgrade the ride of my Ford where I might have been able to save that if I had bought a Chevy. But, I wanted the floorplan, so I bought what was avl. at the time.
I'm not sure about M.Benz Sprinter chassis. Having the cars in the family , I have learned to lease them so I don't have the expense to repair them.
Don't Sprinters have to go to a Sprinter or Freightliner dealership who have the necessary software to clear codes etc. Reading the forums, certain parts of the country can be spread a little thin for Sprinter service. I have heard of owners being stuck hundreds of miles from a dealership. Don't know how true or not . Just something to look into, maybe things have improved over the last year or so.
Regarding the floorplans:
How do they run the lines when you have a kitchen built into a slide ?
I would be concerned about what plumbing or gas lines move or what has to flex in order to deploy and retract the slide. Try to keep things as simple as possible, to limit potential problems that will mean down time for you.
I would only buy a slide floorplan that can be used 100% when retracted. You might have live that way until you can get an appointment for a slide repair.
Make sure your queen bed is really a queen bed 60x80, if that's important to you. Unlike 5th wheels, some "C" floorplans can be a little sneaky if your not paying attention to bed size.