No comments from me re the Audi Quattro as I know very little about that system but have a fair knowledge about 4-Matic after more than 2 years ownership.
The MB 4-Matic is actually not an AWD system. It works in 4 stages that come in very fast (<0.7 sec) when the sensors pick up a slip. There is more to it than this but basically the 4-Matic is a normal 2wd rear wheel drive. That is called "Stage 0". After slip it changes to "Stage 1" ie 35F/65R. More slip it goes to 50/50 (Stage 2). If that is not enough it goes to 50/50 + diff lock on the rear axle(Stage 3). When there is no more slip it goes back to stage 0 again. It made a fantastic difference on ice and snow but sometimes causes repair bills.....
I had it in Sweden during one pretty good winter and when the system works it is like driving on rails compared with 2wd that throws the rear end all over the place during accelleration.

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'90 300TE 4-Matic