Welcome
There seem to be some decent 20vs on the Autotrader at the moment, but also a few that have been around for a loooong time. I'll be looking for another one after Xmas.
20v is probably the one to go for above the 16v if you have the budget. In 1999 they bought in the VIS (variable intake system) for the 20v engine. Also some very late T reg and V-reg onwards, there was a minor facelift on the n/a - better wheels, coloured coded skirts, different grille etc. which are probably more desirable.
Read the buyers guide and check list on here, they cover most of the stuff you'll need.
I had my old n/a serviced at AI, excellent garage.