We've had both gas & diesel motorhomes. 2 diesel Sprinters, 1 C & 1 B, and one gas Chevrolet class B.
If I had my choice in engines I'd do the gas, but most of the B's available that are on the larger size are diesel, so in our case it's diesel, which currently means the Sprinter.
Phoenix Cruiser was mentioned earlier. They are well known for their high quality interiors, and ability to do things for the buyer that is not in their "regular" floor plans, such as moving a cabinet here or there, or different cabinet doors or drawers, or adding outlets both 12v and 120v. Things such as that. They will even build on the 450 chassis if the buyer wants it rather than their normal 350, (don't know about the 2100).
Ultimately you should worry more about the interior and layout, your comfort while inside and driving, rather than what engine type it has.
Those that mentioned the Transit. They are out now and selling like hotcakes from early reports. No RV's as of yet though. Maybe a year out??