I asked this same exact question a couple years ago. If you can do the scheduled "A" and "B" upkeep, then having a dealer around is not as crucial.
Sprinters are pretty reliable. If they were not, the sprinter-source and other forums would be full of posts about this. As far as I read, if one does the proper upkeep (emptying the DEF tank come oil change time), problems are relatively low, other than the issue with long idling and clogging the DPF (a new DPF costs $3200.)
Right now, one has two choices with "B"s. Buy a Sprinter (Freightliner is taking orders for September delivery on the 2014s), or wait until late this summer to see how the Dodge ProMasters fare, with Winnebago's upfit (The Winnebago Travato). If you have time to wait, I'd see how the Fiat... ahem, Dodge vans fare as class Bs, because in Europe, Ducato vans are the most common motorhome type on the roads there. If you wait until next year, the Ford Transits hit the roads, and they are decent vans as well, although I have yet to read about a "B" maker committing to Transits.