One thing that I've always been aware of with car companies like Audi is, if you are going to buy one, make sure that you only buy one that is fitted with an Audi engine, too many Audis are just getting a cheaper run of the mill VW engine fitted into them, and typically that is where the dissatisfaction comes from. Nothing wrong with these other engine options as long as you lower your expectations as what is being sold is an entry point into Audi ownership, or a disposable Audi, which is fine if you are using it as a mega miler and just need to visibility of being an Audi owner.
My only experience of M-B is my SIL who owned as her first M-B a 200 TE I think it was called, ie an estate with a 2 litre petrol engine, it was okay, had really horrid seat coverings both in colour, pattern and fabric, it was an auto and so at maybe 8 years she was advised by an M-B Indie to move it on as these engines suffered badly at higher age/mileage with maybe erosion on the head and the usual M-B failure of auto box intercoolers introducing coolant to the gearbox fluid, not nice, oh and the normally hidden front crossmember corrosion which still affects many of M-B products quietly and unseen until too late. Next M-B was a C class estate in sports set up, good to drive, terrible to sit in as the polished leather sports seats had convex tops so you could not stay still - and it suffered a lot from striking low kerbs due to its sports suspension, it seemed to end up being chopped in for an E class estate with one of the bigger DERV engines, it was a good long distance mode of transport but again as it passed the 6 year mark it really wanted to visit the dealership too often and get treated to lots of new parts, which is not what they expected from M-B, so they headed across to Audi and probably an A6 avant with a derv engine (probably a VW derv engine as her husband was an accountant!) attitude towards new customers was not good from a couple of dealers, absolutely no chance of a test drive in the model/version they had in mind, no returned phone calls which were promised when a suitable car became available for test driving so they thought "F" you Audi and headed across to BMW where they test drove and ordered a 3 series estate with the 2.5 derv engine - and lived happily ever after until now that car has done serious miles and is at the almost 6 year mark, so something new beckons as it likes to be treated to dealerships too often it seems.