Fairly good cars but good luck trying to find one that isn't run into the ground and the price through the roof.
I've been on/off looking for a diesel Jetta for a while now and despite older age and high mileage, the price of these vehicles haven't dropped.
Mainly search used car lots and such. The cars will be clean (I always wonder why people trying to sell a car won't ever clean it), any trim that is crap will be fixed and will have at least had a once over. Also they won't be asking $4k than what the car is said to be worth. To a car lot, its a car...that has to sell. To TDI owners, its a solid piece of gold in their driveway.
TDI club is a GREAT resource but don't bother looking in the "for sale" section. Usually overpriced and ones that aren't are on the other side of the US.
Timing belts and water pumps apparently are a concern with these engines. However if replaced at every 100k, its fine.
Look into filter replacements, I think I remember something about recommended filter replacements.
Look into "coolant creep". Basically, somehow coolant was blowing through a sensor and into the wiring harness on VWs. Yes, this sucks quite heavily.
X2 on the auto transmissions but while I hear about it on the internet, I know a number of high mileage jettas with autos that haven't had a problem, so...
Keep em out of the water. Friend of mine just flooded out her VW when her street flooded. Of course I think that applies to more than just VWs
.
Wheel bearings do go out in these things. Once again, kinda 100k type stuff but just be aware.
They take special kind of VW coolant. Not a complaint, just a heads up.
Like I said, good luck with your search. I never could find one that was in acceptable condition and not overpriced significantly.