Audi Quattro and Subaru are the best systems on the market. Subaru is much cheaper and has better long term reliability.
There are still Subaru GL's and Brats from the late 70's running around with functioning sytems, they are pretty much the toughest AWD on the market.

 

Haldex system used by Audi is built and shares the same systems and equipment found in other vehicles like the Volvo, Land Rover, Mercedes, Jeep GC etc. Its a good system when paired with the more advanced logic like that found in the more expensive vehicles like the Audi, Land Rover etc.

Where it is different than the Subaru system is that they use geared systems where Subaru uses a very simple clutch or viscus coupler system. Over time the more complex Haldex system needs to be rebuilt due to leaking gaskets and needing to be serviced in a manner where the Subaru system simply doesn't require any servicing unless its broken.

They do similar things in different ways except Subarus system is far more simple with fewer parts and requires less attention to servicing and fixing leaky gaskets when the Haldex system needs to be gone through and fixed up again.

 

Haldex systems, with a few exceptions, are primarily FWD-biased. In fact, the Gen1 Haldex transmission only engaged the rear wheels after the front wheels had already slipped. Newer systems have full time 4wd, but are still biased to 95% FWD, with the ability to distribute varying torque bias depending on the car it's in.

Does this make it bad? Not at all. Variations of Haldex units are used in everything from the Bugatti Veyron to Volvos, although I will say only the Audi A3 variants currently use Haldex units. Most Audis use Torsen components now.

By contrast, Subaru's "symmetrical AWD" is designed from scratch to deliver standard 50F/50R torque distribution. Most models use a simple viscous coupling center differential to achieve this. While extremely primitive by modern standards, it is very reliable at factory power levels, and is astonishingly effective at maintaining traction.

The 4 and 5eat, as well as the STI's DCCD system replace the viscous center coupling with an electronically controlled clutch pack, which offers active torque bias control (and DCCD offering direct user control).

Older generation Subarus used limited slip rear differentials, but most (if not all) of the current models have abandoned the LSD in favor of computer controlled wheel braking, which simulates the same effect. Coming from the WRX world, this system seems to be just as effective as the LSDs, and means cheaper repairs down the road (just replace brake pads).

While simple, reliable, and effective, the glaring drawback to the symmetric system is vehicle weight distribution. By physical necessity of the configuration, the engine and much of the transmission is located entirely forward of the front axle, lending to a heavy front bias on all Subarus (BRZ excluded). I'm not sure how many people on here AutoX, but in the WRX world, this leads to catastrophic understeer. Subaru will say the lightweight and compact boxer engine improves this problem, which is true to a certain extent, but weight balance will continue to be a factor for as long as Subaru maintains this configuration (i.e. forever).

 

Think of the weight distribution challenge as the opposite physics issue Porsche has struggled with since they created the 911 - the weight of the engine in the back of the 911 even today poses an interesting twist to how the 911 handles at the outer limits of tire grip. They don't put wider rear tires on the 911 because of the massive amount of power sent to them. They put wider tires on the back to help keep the weight from the engine swinging the back car right off the road.

Most people don't realize the Porsche Caymen with its mid engine design is actually a superior machine vs the 911 when it comes to handling at the outer limits.

 

Which Subaru system? There are many and they are all slightly or very different depending on the model they are equipped to.

Haldex is not traditional Quattro and it is only used on transverse models (read FWD based models)(A3, TT) from VW and Audi. A4 and everything up uses Torsen which is much better. The only VW product to have Torsen is the B5 Passat and it is fantastic in the snow. Everything else VW that is 4motion is Haldex, including R model Golfs. There are boxes available to give the Haldex in R models more sporting feel but it is nowhere near what Subaru or Mitsu offer.

For example, the wife's inlaws have an '08 Volvo XC70 with Haldex (they also have a Passat wagon as previously mentioned) and it is a pig. Very FWD bias and heavy on the understeer compared to my 3.0R Outback. The Volvo doesn't allow fully defeatable TCS either.

 

Wow! thanks to all that have replied. Now, i was considering a wrx-2013 is that awd system different then lets say a legacy of the same year? Also, a general question, if all of us didn't have the choice of subaru's what other car make would u decide on and why? are there other cars that are just as good as subaru's. I live in a state (OHIO) where we get a ton of snow each year, so if wanted to go with another make that was pretty good in the snow as the subaru, what make would that be?