You will read things going either way. If you want it from the "horse's mouth", I'd go to the Sprinter Source forums for news either way. Same with the Ford Transit and the RAM ProMaster.
As far as I read on the owner's manual, each 10,000 miles, you have an "A" service, then a "B" service, alternating between the two.
As for reliability, none of the vans sold are garbage. There are a lot of miles on each van. The US is also Mercedes's #1 customer for Sprinters, so they are not going away anytime soon.