Trailer hauler

For fuel economy, the TDI is the way to go.

How heavy is the trailer? I have no experience towing, but friends who tow tell me that a long wheelbase aids stability. Those who tow somewhat heavy trailers tend to prefer the large GM and Ford SUVs. The Dodge Durango is one in-betweener, longer than the Touareg but not nearly as bulky as the big ones. The related Jeep Grand Cherokee is offered with a diesel, but it's also similar in length to the Touareg.

How heavy do you want to haul? If it's less than 5000 pounds, there's a lot of choice, but over this, list is much smaller !

I agree with the earlier comment recommending the Dodge Durango. The Durango is rated to tow over 7000 lbs like the Touarge. Not knowing the trailer weight is the unknown here. Many vehicles are rated to tow 5000 lbs (Toyota Highlander, Chevy Traverse, Ford Explorer).