I would be hard-pressed to give up the maintainability of the Ford for an MB. We have two MB vans at work that seem to love the attention they get at the local shop. I can't speak to the comfort of the cabs. I do know that the E-350/450 cab can be a bit cramped, especially on the passenger's side. I have an E-450 Coachmen Concord 300DS and love everything about it. However, we needed more room and carrying capacity to allow for 3+ adults and a dog. My 84-year-old MIL is traveling with us and the Concord doesn't have a second suitable bed. So we have "upgraded" to our Itasca Meridian 34.
I know that most of the E-based motorhomes have a pretty generous CCC compared to the MB.
Aaron