1.9 tdi's are the best 1z's/pdi's these go on forever and i've had 250k one's loads of times with no issue's. pd's can be remapped easily for really good power, my 1.9tdi passat pd is around 170-180bhp now with 186k on the clock

the 2.5 etc v6's are problematic and cost in the long run unless you are careful, same with the 2.0litre tdi's that i've seen people own and garages work on.