BMW has used ZF auto-boxes since G was a pup. And they're NOT very good units. Late model ones are better, but they have all kind of running problems, and life expectancy is barely 100,000 miles.
Also on the BMW, be wary of the timing belt, as a leaking water-pump will cause the belt to fatigue very quickly and snap.
The E36 can have rear suspension mounting point problems that result in the rear suspension coming loose from the car. More prevalent in hard-driven examples, but happens on others too.
I thik by 1996MY BMW solved the profile gasket problem, but don't quote me on it. And BMW will offer NO goodwill repairs on those cars. Yer on yer own.
The E36 3-series interior is smaller than the C-Class, especially in the rear. If you ever plan on carrying people back there, then you'll need a bigger car. I'm a proponent of small cars, but the E36 is really cramped back there, even in sedan form.
On the plus side, the 328 depreciates more, and as a used car is a better buy than the MB. A manny-tranny is available, but watch for abuse. Many 3-series cars are owned by club-footed street-racer wannabees.
BMW parts for routine maintenance are priced similar to MB, but true repair costs can be higher.
I like BMW and Mercedes, and consider both excellent choices.
1998 C230 "Black Betty"