There are a whole lot of factors when comparing Sprinter against Ford/Chevy. These are the two that turned out to be the most important for me:
1) I couldn't stand the tiny leg space available in both front seats of the Ford, and the Chevy is only slightly better.
2) I could not find a single Ford/Chevy with a slideout where I could put the driver seat back far enough to drive comfortably. By comparison, in every Sprinter I looked at I can put the seat back further than I need.
The increased mpg is icing on the cake, and the Sprinter RVs tend to be 6 to 10 inches narrower, nice on narrow roads. The Sprinter AFAIK is the only Class C chassis where the sum of the GAWRs exceeds the GVWR, making the Sprinter the only one that you can load to GVWR without busting a GAWR.
Not having had any major mechanical problems yet, the cost of ownership has been pretty much the same as with the other brands. Some of the Sprinter owners have been plagued with recurring mechanical problems that turned into genuine nightmares. Some of the Sprinters were delivered with Kumho tires which are prone to blowouts. Others have Continentals which are doing well. For replacements, Michelin is the overwhelming favorite. I believe the greater percentage of the Sprinters have been reliable. Getting a bad Sprinter is probably more painful than getting a bad Ford/Chevy.