Those models years are still pretty new, so reliability data might be based on sketchy information. Edmunds only carries reliability data up to 2009, for this reason. Just about any car can look good the first year it is out, for instance.
I would suggest that you drop into our M-Class Owner's Topic
. You will have to scroll backward to read older posts but you may find the information and experiences from other people helpful to you.
Keep in mind of course that this is only a small sampling of owners, and that many happy owners don't necessarily come to the Internet to post their satisfaction---often they come to seek assistance on a problem.
There have been two recalls:
Campaign No. 2012070002, September 2012
This Service Campaign has been initiated because Daimler AG (DAG), the manufacturer of Mercedes-Benz vehicles, has determined that due to the settling properties of the seal, oil may leak from the camshaft adjustment solenoid. Dealers will retrofit four adapter harnesses onto the engine wiring harness as a precautionary measure at the next workshop visit.
Campaign No. 2011050006, June 2011
This Service Campaign has been initiated because Daimler AG (DAG), the manufacturer of Mercedes-Benz vehicles, has determined that the underfloor crossmember seam seal may not meet specifications.
Dealers will correct the underfloor seam seal at the next workshop visit.
There have been a fair number of TSBs on various issues, so I'd say the vehicle has not been entirely bug-free. Some are quite minor, like moisture forming in the headlights, or a tight seat belt tensioner. The most frequent seem to deal with harsh shifting of the transmission and various clunks and groans in the suspension when going over bumps.
Hope this helps!