I am sure opinions will differ but here is mine:

The earlier version of 4-Matic was quite trouble prone due to it's complexity.

The newer (as in W210 +) version is very simple and quite reliable. Basically a typical gear transfer case splitting power approx 30/70. No fancy clutches or fluid packs. Slip control is at the individual wheels and uses the ABS braking circuit.

Yeah, I know, oversimplified, but I do not feel like writing a book.

Of course there will be exceptions, but mine has been flawless with 70K miles and counting. It worked great with our latest snow storm.

Best Wishes,
Ron