Touareg TDI vs X5
I test drove the 2012 Touareg TDI extensively before settling on a 2012 X5 diesel. In my opinion, TDI has a smoother and more quiet engine. TDI is also more practical with more trunk space and back seats that slide forward. It also gets better mileage, probably due to the 8 speed tranny.
Other than that, IMO the X5 is better in every way. In no particular order: handling, power, interior, looks, fun, you can pretty much build your car the way you like it, warranty, maintenance plan etc.
Like you I was looking at paying about the same for a TDI than for a X5. In my opinion, the X5 was a better value.
Despite the above, the Touareg is a fine vehicle. Anybody looking for a diesel SUV should have it on their test drive list.