I have a 96 with the M104 motor.
Current mileage is at 207K miles.
Never had a W124 so I can't do a comparison but for the most part this car is reliable.
Parts and labor is expensive compared to Toyotas/Lexus.
Have done some of the minor maintenance items but some of the majors are pricey.

No problems with the following:
rust, dash, head gasket, spring perches, wire harness, transmission.

Problems with the following:
Window regulators, AC Compressor (just went out at 206K miles)

If you can find a 96-97 and don't mind the having less bells and whistles, go for it. It will last a long time.
They are also reasonably priced now.

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2010 W212 E350 Sport
1996 W210 E320 (220K miles)