or are there differences. if so which is better in snow, rain, etc.

The 4motion system uses a Haldex clutch. It is primarily front wheel drive, but send power to the rear when needed. Also the engines are in a different orientation.

The quattro system is permanent four wheel drive, using a torsen diff for the centre. Better system!

the subaru is more like quattro, permanent 4wd

VW models with transverse (east-west) engines, such as the Golf, use the Swedish haldex awd, an electronic approach. VW models with longitudinally-mounted engines (north-south) such as the Passat use quattro, a mechanical approach. Have I got this right?

the Passat 4 motion is over 65% Audi in parts. The 4 motion is supposedly the same as Quattro but a generation back. The Passat is setup for a softer ride. It handles nice but the A4 is much better.

AWD for Audi, 4Motion is used for both the TORSEN and Haldex types of AWD for VW. In the Passat/A4/A6/etc with longitudinal engines, the system is TORSEN and identical across the brands. Same for the Haldex systems across the platforms with transverse engines.

Answer your questions?

suspension, not drivetrain.

Understand what determines the ride, just making a editorial comment on the difference. Here is a link to a site that discusses AWDs<ul><li><a href="http://williamtoll.com/quattro_info.htm">http://williamtoll.com/quattro_info.htm</a</li></ul>

"Until the all wheel drive Audi TT arrived the Quattro abbreviation meant the same Awd system regardless which car carried the badge. Now Quattro is just a trademark and there is a lot of confusion. Audi TT Quattro used Haldex Awd system, Audi A3 Quattro uses viscous coupling system similar to Awd system used on VW Golf Syncro. But there is "real" Quattro system used on VW Passat 4motion, although adjusted in some other way, as the representatives of V.A.G. said. But this new beautiful name is nothing but another trademark. VW Golf IV 4motion uses Haldex system."

If you read the part on the Passat it seems how it distributes power left to right is a bit different from Audi<ul><li><a href="http://williamtoll.com/quattro_info.htm">http://williamtoll.com/quattro_info.htm</a</li></ul>

I read a lot about Audi's quattro systems (Torsen and Haldex), but not about Subaru. Who or what web-site has a good explanation of their technology? Is it comparable to Audi? Better/worse?
I read something on subaru.com, but it stops explaining where it gets interesting, I cannot understand how the central differential works. They claim however it is very special ...

There you go, this might help.<ul><li><a href="http://www.california.com/~phdarch/awd.htm">http://www.california.com/~phdarch/awd.htm</a</li></ul>

On most of the automatic models it is electronically controlled. The torque split is 90% front normally. In fact rear drive can be disabled by jumpering a conection under the hood. It's good but less effective than the Quattro IV system.

The manual models are different and I think use a viscous coupling for a more even torque split. These are quite effective!

The Outback VDC model is different again in that it's an auto only but has something like a 55/45 torque split and a wider adjustment range. I haven't tried this but wish we had before muying our H6 Outback.

A viscous coupling uses a compound that changes from a fluid to semisolid when agitated (friction). Assume the front wheels are normally driven. As long as the F &amp; R are turning at the same rate, it remains a fluid and the F&amp;R halves of the coupling are independent. If a speed difference develops between them (because the driven front is slipping), the fluid thickens instantly and acts like a clutch so power is transmitted to both F&amp;R. When the speeds match (uniform F&amp;R traction regained), it becomes fluid again decoupling the F&amp;R.