BMW > Audi > Merc.
Driven all but audi on a regular basis. MB is more unreliable than BMW and often less comfortable for the driver. BMW is refined, feels good, but not as "friendly" as the MB.
Also, MB here has a superb service department, which makes going in so often less painful. They are more than willing to comp repairs caused by stupid design flaws (comped $4000 of gearshift selector work from spilled drink due to cupholder flaw) and they are very nice, but the cars just don't feel as well made.