Had a few MK4 Golfs over the years, well me and the Mrs 😉
The GT-TDI are great for economy as well as safe overtaking performance.
I have had both the 150bhp and the 130bhp, which are both good.
You are not going to win any handling competitions, but great motorway mile muncher, I get near on 55mpg at motorway speeds out of my current gt-tdi.
Common problems to look out for-
Plastic blades on oil pump can give up, replace when you have the cambelt done with the metal blade version (70k service).
Electric windows motor fittings can play up, will drop and then jam.
Some have problems with the MAF sensors, but I never had a problem yet.
Spare keys are expensive to replace, so make sure it has two working key fobs.
The MK4 Anniversary GTI versions are desirable, just watch out for copies if you go down that road.
Now if you know where there is a nice MK4 180bhp 1.8T GTI Anniversary going let me know 😉
Its the only MK4 GTI I would go for.