Barcelona will definitely beat Napoli, Walter Mazzari is not even the man for Napoli, this are just try and error coaches, for long term, you need a better and tactical genius for that club.
the situation might be different when Napoli's performance is like last season, with the same players and coach. but the situation is different, Xavi and the Barcelona squad will be more favored to win in advancing to the next round.
The tightest competition is probably Inter's match against Atletico Madrid. and there is a possibility that the last 8 rounds will bring together strong European teams who are favorites in the Champions League.