I've just switched from BMW to Mercedes, so here's my take.
I had a 318 E90 for 4 years, finance was up, didn't like the new shape 318, absolutely loved the look of the C-Class in white with the pano roof, so switched to Merc 3 months ago.
So out goes 2.0l 318 Manual, and in comes 1.6l C-Class Auto.
Disclaimer! Note I am comparing a 4 year old E90 with a spanking new Merc....and the Merc is auto box compared to BMW manual.
The 2.0 BMW gave better MPG than the Merc is, and for a saloon, the BMW handles like a coupe, great round bends.
Apart from that,
The build quality and finishing on the Merc is a whole level up from the BMW.
The ride in the Merc is far superior over rough surfaces, ironwork, speed cushions, etc, but not soft through bends.
The performance of the Merc is noticeably superior to the BMW, even though the published BHP only shows a difference of around 10.
The engine runs noticeably smoother in the Merc.
The 7 speed auto box is an absolute JOY and I am loving it. I have no experience of BMW auto's, but this is extreme driving pleasure.
Intelligent bi-xenon headlamps, they are remarkable.
My history is VW Scirocco x 2, BMW 318 x 2, and now Merc. The Merc is hands down the best car I've ever driven.
2008 E90 318 ES Edition T.Silver