First, they fixed a lot of the problems with the turbo diesel since 2002.
Drive a TDI. The grunt is incredible. The mileage is too. A turbo diesel begs for a manual transmission, though (just the driving dynamics - they can certainly be used with an auto). VW diesels require very special oil. Desel is more expensive and harder to find at the corner gas station.
It's hard to justify here because they cost so much more and diesel fuel costs more than gasoline. Not so in Europe (where both are atrocious).
Diesels last forever, but the car will fall apart around them, and most people don't want a car forever.
Any reason to consider the TDI instead of the GLI?