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The VTD-AWD is the very best AWD from Subaru. It also splits torque 45/55 front/rear through a Torque-sensing Planetary gear center differential and works along with a heavy duty 6-plate continuously variable electronically controlled clutch-pack. It is conceptually similar to the AWD employed in the Audi A8/S8 and other V8-equipped Audi Quattros. The Quattros employed by other Audis are not as sophisticated or effective. It is also employed in the World Rally conquering Subaru Rally cars in a much heavier duty form . This system acts with brutal directness (since it is a mechanical system) and is extremely fast in acting during slippery conditions and has a broad range of torque transferability (front/back back/front), when compared to the other 2 systems below.

Next in line in effectiveness, would be the Active AWD present in all other Auto-Subarus. They do not have the Torque sensing Planetary gear center differential of the VTD-AWD and have a lighter duty 4-plate clutch pack.

Then comes the simpler VC (Viscous Coupling) AWD of Subaru also called Continuous AWD that uses a Viscous Coupling (coupling filled with viscous fluid) as the center differential. It is a reactive system and in slippery conditions, needs slippage before it can act, hence the reaction time is slower than either of the above systems. This is used by all the manual-Subarus including the manual-WRX. Not as effective as either of the above systems but is better than the 2nd system in some respects due to the 50/50 torque split in pretty much all normal driving conditions.