This is interesting. I used to be into BMW in a big way but got sick of their hideous reliability and scary handling into bends.
Sadly I am temporarily burdened with a 2012 3 series at the moment which at this very moment in for repairs on its stupid tyre pressure system.
BMWs owned are x2 328, x1 M3, x1 2.8 Z3, x1 316 compact, x1 320 (current)
My 320 is very twitchy and I drive like an old woman round every corner.
My limited experience of Mercs on the other hand has been great handling and bar niggles like the roof on my SL and gunked up windscreen wiper (on a car that had been siting) very good reliabilty.
I might add the BMW i have had have all been new or a few years old. (Compared to 10 year old + mercs) and yet I have had two engine failures, head gaskets etc etc
Stll want an E30 M3 or E34 M5 though!
I had a 318is coupe in NZ, whilst slow it handled like on rails which helped hide the speed and didn't cost us a cent, in fact, I made $400 on the sale, amazing what a good cut and polish can do.
Had a 525i as well that apart from a fuel pump at 190,000kms, was reliable too, and then here in the UK, my 528i Individual was awesome, had the usual hedgehog problem that cost me £19 to fix myself, had the auto flushed (for peace of mind) but nothing else went wrong or cost me money to repair/replace. It handled brilliantly and filled me with absolute confidence, admittedly it had good tyres on, Avon ZZ3s all around (and I really don't rate the Pirellis on the Benz), it sat low and squat, didn't roll in the corners and just gripped.
I sold that to a friends mate who is now selling it back to my mate. I sold it at 147000 looking like new, and he is now selling it on at 165,000miles, still looking like new, but has had a new temp sensor and ABS sensor fitted, so only maintenance really. All in all, a brilliant car and fool on me for selling it.
I think for me, whilst the merc is not necessarily scary, it just doesn't fill me with confidence, mainly on the front end, so perhaps new tyres will change my mind, but I think even my Mondeo ST220 Estate handled better than the Merc.