Over the past 20 years I have owned a preponderance of MB's 450sl, 450sel, 2 300e's, a 190e 2.6 and now a 400e. The only new one was the 190 purchased in 1989. Generally, I find it insane to buy new but that's another post all together. Interspersed thru the years have been a few BMW's and Porsches ... an M635, probably my favorite car of all, a couple of 325's, an '89 750il.
There is no doubt the BMW's have a sharper edge for the performance oriented driver. Both cars have a very distictive feel and it is quite different, so, as has been posted earlier it really does come down to personal preferences. If you told me we are going to spend the day running at 9/10's up an empty HWY 1 from Morro Bay to Carmel I'd be most likely to jump into a BMW. If you said pick a car to live with as a daily driver ... I'm in da' Benz.
My personal judgement is the MB is a more easily handled DIY maintenance proposition and probably a lighter load if you have all the work done by a shop or dealer as compared scenario by scenario with the Bimmer. But I wouldn't fear either one.
I spent 4 months in search mode leading up to my recent purchase of the 400e. I had in mind a BMW 540 or 530(because I still prefer a manual trans)or a 300 or 400e. Those model bimmer's were produced from '94 forward, the 300e forever and the 400e from '92. I did not want to spend more than 14 grand ... now you know why it took 4 months. What I found was a lot of really abused, hi mileage 540's and 530's without books and records and even then 15-16 grand seemed to be the number. I found lot's of nice 300's back to '87 under a 100k miles I would have been very happy with. Many of them in the $7-$9K area. (but I wanted a passenger bag) Can you imagine a better car for that kind of money? I finally succumbed to the siren song of the V8. I bought a relatively well maintained '92 400e with 95k on the clock, had it checked by a competent independent shop (most Benz dealers will no longer do pre-purchase inspections citing liability issues). I paid $11,500 for the car. I calculate I need to put about $1500-$2000 ... shocks, leaky power steering pump, either a trans or diff mount or a driveshaft center bearing and frontend bushings. I can probably halve the cost at least if I extend myself on the DIY end. So I am in the car maybe $13,500 tops. Let me see? A mechanically perfect 400e with flawless paint(almost) and a pris, unmarked(now, thanks to Leatherique) full leather interior or a Daewoo? Uhhhhh ... I think I'll take the Benz. Based on my personal needs/wants I have about 8/10's of all the performance of the 540, about 14/10's the cache, elegance and comfort. More interior room. I also have a car I can do much more of the maintenance on than I could on the 540. I think I'll be very happy with my decision for the next 6 years or so. I KNOW this car will go 200k.
There is no doubt both cars are wonderful, joyous machines which take getting from A to B to a level most do not understand. Appreciate them both, drive what best suits you. No one's preference or opinion is as meaningful as the one YOU get sitting behind the wheel. Ain't it wonderful the choices we get to make?