Hey,
Mk4 tdi is definatly a good decision!! I bought a 52 plate 130 pd last Jan. Its the best thing i have ever bought. 6 speed , loads of torque and very nice to drive. I can't say I have had any problems with it at all. the mpg is amazing when you have that kind of performance. If your going to be looking I would look out for cars going cheaper than they should be!! there's usually only one reason for this and that is they have been bumped or trashed about.
I do regular work on behalf of a VW main dealer (Paint repairs) regular bumper scuffs are nothing to worry about but look out for suspicious paintwork on doors bonnets and 1/4 panels.
Also if you get your ideal buy, I'd recommend going to the likes of Jabbasport.co.uk and getting your car re-mapped. its about ?400 but that will be the next best thing you ever bought.
Lots faster................better economy generally.
Mine now keeps pulling after 3000 rpms 197 bhp
Hope this helps.
Gary