Hi Buffy. Although the 16 valve 1.7 Alfa 33 engine may sound enticing - having fuel injection and 138bhp, compared to 118bhp of the 8 valve 1.7 engine, it's not as nice an engine or as effective because it isn't very torquey low down the rev range and demands high revs and last second gear changes to get the most out of its power. On the contrary the 8 valve version has a smoother range of good torque throughout the rev range and it still can be reved pretty high if required. I've read this many times and also heard it from some key characters of the Alfa race world.
Like you I also had the option of which one to go for but my mind was easily made up once I learned about them. My Alfa engine is the 8 valve and I've had it re-built and breathed upon, including with some 16 valve parts. I've been told it will push out about 140bhp which is more than the 16valve so for me it's a win win.
Giles