Originally Posted by sibhusky
The Audi system is better in that it has a torsen whereas the 328 has a mechanically based transfer system. However the mechanical has less moving parts and does not rely on a stepper motor which can fail or produce weird electrical gremlins.
I think PTinVT meant that the BMW has more static bias to the rear wheels much like the Porsche system during normal driving unlike the Audi which is more neutral or front biased.
The only thing you need to keep up on with the BMW x drive is replacing the transfer case fluid which is pretty simple,every 50k or whatever is recommended.
I think you need to read some current Quattro info. You have it backwards. I think the TT may still use the old neutral/front bias but A4/s4 etc haven't used that for years . BMW is currently light years away from quattro re high performance awd.