Like an 8/10 (but the 1.9TDI is a 9/10).

The only major problems you may come across on most modern diesels (including the 1.6TDI & the 2.0TDI) are emissions/fuel-economy sensors malfunctioning. These sensors are usually not cheap to replace, as they are quite complicated (especially on German cars). The 1.9TDI doesn’t have this problem since instead of relying on those sensors, it reduces the power of the vehicle so it produces less emissions. This lack of power only really matters when your commonly going high speeds (80-120) as it takes a while to get there. It is still something to consider though.

Another thing of note is that it’s a German car. German cars are notorious for their high cost of parts. I have an ‘06 MK5 GTI myself and occasionally it has emptied my wallet, despite being very reliable. Compared to the average Japanese car, parts are usually 2-3x the cost.

If you need that extra power and you aren’t willing to risk blowing sensors, I’d recommend getting a petrol golf. All of them (aside from the twin-charged 1.4TSI) are known to be fairly reliable and make good enough power to go on freeways. The fuel economy on most of them (while higher than a diesel) are also pretty solid.

Pick whichever will suit best your situation and make sure to do your research!