Dale,
As with any car look for the lowest milage example you can find for the best price. Yes, Golf's can take the milage very well, but there's plenty of 70 - 90k cars going; so be patient. I got a silver 3 door 'digi' GTi with 70k for a little as ?800 - she was mint and not being sold by an enthuiast, so got a bargin!
8 valves generally are easier to maintain and last a bit longer, although on paper have quite a bit less power. As the 8v has to be revved less to get the best from it they'll take the miles better too (how many 16v have valve stem oil seal problems compared to 8v's??), but if it's the power figure that means the most to you then choose a 16 valve without a doubt.
On the other hand, get a good 8 valve with air box mods and a chip and you'll easily keep up as many of us in here can vouch for, or kick some 16v ass
Both are cracking cars and if your not really fussed about the figures, forget the whole 8v vs 16v and buy the best example car you can as 'mint' cars will only ever go up in price for the next few years - then on to proper 'classic' status!
Hope this helps and if you've got any more specific questions feel free to ask ....
