I prefer the 16v to drive, the 8v engines can feel very flat, especially the later Digifant ones.
Look for the usual "old car" issues (ie being generally knackered) but weak spots are rust in the sills, door bottoms, boot floor, tailgate; rings (look for blue smoke under full power); distributor issues on the 16v (look for an oil leak at the base of the dizzy, this can be expensive to sort out and leads to rough running); knocking top mounts (cheap to fix) and non-functional handbrake (you will nave to replace the calipers with new or refurbished ones and they always fail again after a few years)
Amazingly well catered for in both the aftermarket tuning world and for just general spares - GSF and Euro Car Parts have almost everything available at decent prices, particularly suspension parts, steering, exhaust, brake and most other general running gear. Even VW are reasonable for some parts.
If you are going to buy a 16v one you will need to rev it quite hard to get the full benefit of the extra performance whereas the 8v can be hustled along at a decent pace without too much bother.
PS I am not a Golf fanboy in the slightest! In fact I really didn't like the GTi I had very much at all. The handling was too predictable for my liking and I never got on with the feel of either the gearchange or the steering.
It's funny, compared to the 205 GTI I found it felt cumbersome and high-sided, but gruntier and had more mechanical grip.
My Golf-loving mate tried the 205 GTI and found it felt gutless and like it was about to fall off the road at any second, but much more flickable.
Depends what you want in a hot hatch - the 2 manufacturers just found different ways of skinning the same cat.
Looked alright though: