I always said if I was getting one it would be the 16v turbo as you can buy more tuning gear for them and see some good power.
However my mates recently got a 20v turbo, and **** me its quick. Its hard to explain, but it has 3 power bands in each gear. Still never been in a 16v turbo, but after being in my mates 20vt I wouldnt bother with the 16 anymore.