The only difference is the power of course and you get Alfa's DNA system on the 16v which you don't get on the 8v (bit of a surprise when i picked mine up and it wasn't there)
78bhp doesn't sound a lot but she is still fun to drive and pulls well if you have the money get the 95bhp if you don't want to spend an extra 1k get the 78bhp either way you will have a big smile on your face when you drive.
the 95bhp sprint was a limited edition to promote alfas link up with british athletics, that engine has been replaced by the normally aspirated 105bhp multiair engine, the 78bhp version is the normal production model, i think even for a small car the 78bhp seems underpowered but some people on here have said that the same engine is fitted in the fiat grande punto and it performs fine, i have the 95bhp engine in my lusso and its great for everyday use, even on longer trips it can cruise at 70/80mph all day, the 78bhp has start stop which speaking for myself i would rather not have, it all comes down to which car you can get the best deal on.
I would get the 95BHP. I've never been keen on small hatches with >90BHP. My old Corsa SXI was around 90 and was just quick enough to be useable on motorways etc. Unless you're under 21, I'd go for the 95bhp, especially if you're getting the bigger discount.