Do you take them to M-B dealers for maintenance? the ones around here are all clueless.
As for going with a Sprinter, I do believe many are swayed by the badge on the front grille. In 2014, we needed another van, and I knew the Transit was coming, but not available yet and didn't want to get a now dated E series. So we bought a Sprinter to try. What swayed me was the sweet 4 cyl diesel power train with 7 spd auto. it seemed like a winning combination and proven power train. On top of that, they offered 3 years, 60Km FREE maintenance.
Sorry to say, but we experienced all kinds of problems with it starting in the first year. problems with sensors, oil leaks, air condition failing, mystery lights on the dash lighting up, problems with the emmission system, and Im sure others I can't think of right now.
When researching this van, I was impressed with its "20,000km" service interval. But what they don't tell you is that every time you take it in, they find something wrong with it, and I leave with a thousand dollar invoice.
With the Transits, i spend $60 on an oil change, and the odd $200 for a brake job once in a while. Other than that, they have been flawless.
Rust has not been an issue thus far on the Sprinter, if I did my research correctly at the time, they "fixed" the rust issue starting from 2014 model, otherwise I wouldn't have bought one. If I recall, they started using galvanized metal or pretreated it somehow, and they sprayed rustproofing on the inside of the panels I think. I can't remember full details, but the description seemed like they took proper steps to stop the rust.
Sorry, but my Sprinter experiment is done, won't touch one again. We went with an 2018 Transit this year, and will definitely be buying more in the future.