I have owned both recently, BMW 04-06 and now MB. I think both of them have their pros and cons.
Both are awesome in how they stick to the road, BMW's are slightly better on the curves, but it mostly depends on the type of tires you have. The engines although lack the horses (Non M's and Non AMG's) which other companies offer, are very reliable. suspension is great. Exterior styling is mostly very attractive (you pick depending on your style)
MB - Hate the transmission. The lag in changin gears and specialy from gear R-D or D-R is LOONG!!!
BMW - Great transmission. less lag time
MB - High quality interiors/ dash / seats
BMW - Low quality interiors/ dash / seats
MB - Very unreliable electronics
BMW - Somewhat unreliable electronics
BMW - Good Warranty, cover maintainance
MB - stopped covering maintainance in 2004
Almost same price range.
When I was in the market for a new car, I picked MB over Bimmer not because BMW lacks something, but just because I wanted a change. I think both are great brands and make quality cars. It would be your personal preferance with what you wanna get.
ALthough I hate the cheap electronice that MB has and also BMW, small things that you do not even think will go wrong, do go wrong in these cars.
Like in BMW, my sunroof shade stopped working like 4 times in the 2 years I owned it, the clips it slides on will just break. Few times, my passenger side door refused to open from inside, and couple time from outside. This once happened with the driver side door too, but after restarting the car (Just like a windows PC) everything worked fine. Once, all the windows rolled down themself. My 325ci, with all options and packages, came without, WITHOUT a security system, can you believe that?? even a civic has that .
Coming to MB, after 1600 miles on the car, the passenger side window would not roll down. after 2300 miles, ESP malfuntion message came on. After 3000 miles, roof stops in middle while opening or closing. and I only have 4k miles on the car.
So you make the pick, just keep in mind which ever you get make sure you HAVE warranty on it, caz these things are expensive to fix. Brother just paid $1600 to fix his AC on his MB.