My Nephew has a 2010 C300 4matic and I've driven it several times. They are nice looking cars in my opinion(As are BMWs depending on a person's tastes). Interior ergonomic seems to be better setup than a BMW EG. Cupholders location, seat/door controls in one section. It's seating is comfortable ( as long as your in the front of course). Cruise control function/placement is just as stupid as the E90s.
Depending on your need, if you want comfort, decent power and a "nice" drive Mercedes might be for you. The 4matic is definitely not anywhere near as good as the Xdrive in BMers (my nephew stated that) so you might consider snow tires if you get a Mercedes with 4matic.
If you want a tighter ride, excellent handling, good power and more of a sporty drive, BMW then. I decided on BMW because the Auto Transmission(AT) in Manual mode blows away the Mercedes AT in functionality.
Both will be expensive to repair, parts, need Premium gas etc.
That's my 2 cents.