As you well know, the internet has provided many forums for disappointed owners to say what's gone wrong with their vehicles, and if you read their posts, you're likely to come away thinking that reliable vehicles totally vanished, oh, about the time internet forums caught on.
In truth, any modern vehicle is so full of computers, electronics, etc. that at some time or another a sizable proportion of any model will have issues. I think the overall accumulated wisdom on the Sprinter is "pretty reliable overall, and very reliable sometimes" (lots of 300K mile Sprinters still doing fine),
BUT when they do go wrong, you are faced with expensive parts and service from a small number of, in some cases, undertrained dealerships that can supply the knowledge and diagnostic equipment to get things fixed.
The change several years ago from having Dodge dealerships selling and servicing them to some, but waaay short of all, Mercedes dealerships made the problem worse. There are, for example, in the Portland, Oregon, metro area of 2.3 million, no MBz Sprinter dealers. And the Mercedes dealerships that do handle Sprinters have mechanics with relatively short experience. The backup plan in some areas (like Portland) is that some Freightliner dealers sell Sprinters and have dedicated Sprinter service facilities, along with experienced mechanics, since Freightliner has sold Freightliner-badged Sprinters--regardless of nameplate, all Sprinters have always come from a Mercedes factory, BTW--continuously since the first North American importation. But Sprinter Freightliner dealers aren't very prevalent, either.
A lot of us were, therefore, eager to see Ford (Transit) and FCA (Promaster) release North American versions of their European vans. We were hoping for both lower prices (with the Transit being kinda disappointing there) and a way bigger dealer network (good there) with many well-qualified mechanics (which may take a while). In truth, all three vans--four, if we throw in the Nissan NV3500--have strengths and weaknesses, but the Sprinters have always been a treat to drive, and the reports coming out suggest that the Sprinter is the most sophisticated and still gives the best driving experience. But you will not generally have lots of alternatives for service.
If you haven't already done so, head over to
http://sprinter-source.com/forum/ for all the information and opinions on this topic that you'll likely want to process.