Both of them kicked major a$$ this year but when I say M-B is getting its lunch eaten, it's by judging on a momentum scale. If I'm not mistaken, it wasn't until last year that M-B had been outsold by BMW ever(?), and if you look at worldwide sales M-B is losing massive market share to not only BMW, but now Audi (whereas a couple of years ago they were in the lead, now they're falling to a distant third rapidly).
However, for me it really doesn't matter, as the same goes for when I had an M-B: For all I care I'm happy if the "other guy" sells more, since it doesn't have to make me see myself come and go as much as possible.
Yeah the deals were insane and it's nice to see many of us benefited from the BMW/M-B ca t fight.
However, I'm pretty sure M-B's incentives were what pushed BMW's incentives so much in Dec. People have been getting W212's all year for under $500 a month and with practically nothing down. I think it was M-B who had the first 24 month Lease with an artificially high residual to move a massive amount of E's in Nov, of which BMW retaliated in Dec (and ironically sold about as many 5's as E's sold in Nov, reversing the tables as the E sold significantly less than the 5 in Dec while it was reversed in Nov).
Still, however, from cross shopping these two cars a lot, I can say even by getting my own Lease incentive that is better than anything I had imagined on a loaded 535i, it still doesn't match how cheap W212's Lease for (again, in the $400's with minimal down is just crazy subsidized for a $50+K MSRP car). Then again, I don't follow 528i Lease rates....