The Touareg won the recent Car And Driver diesel SUV comparison test over the other vehicles you list as well as the Jeep and Porche Cayenne. I tow approx 4,500 lbs with it. I think my tongue weight is in the 600 lb range with my 2 heavy 6v batteries and full propane, but I don't know for sure. I tow with a full water tank too because we never camp where there are hookups and I don't like having to search for water. I believe that using a WDH is not optional. Without it the steering is very light and the rear suspension is overloaded. I average about 14.5 MPG towing.
APT wondered about GVWR being exceeded with a lot of weight on the bumper. That would definitely be true, but we have the stripped Sport+Nav version, and the 2 people + 2 dogs weigh about 360 lbs. We carry NOTHING in the vehicle with us. Everything is in the trailer.
For our situation, it is an ideal TV, but if I had 1,500 lbs more to move I wouldn't personally want to use the Touareg. The hitch is only rated to 616 lbs, and you will need to distribute more weight with a beefier WDH. Yes, I know a lot of people do it, but it is going to be hard on the vehicle. Get the right tool for the job and if you must have that bigger trailer maybe you should get a truck and park it outside.
BTW, VW has conflicting information regarding the use of a WDH on the Touareg. The hitch clearly mentions using one, and the manual suggests that you should not. Some have made modifications to the hitch gear by welding stuff onto it, but the bottom line for me is that it works great and I haven't had any problems with it. I've even had the bumper cover off after someone hit me and there were no indications of stress.