When I look at the matchups I think that the most difficult to predict result can the Napoli v Barcelona and Inter v Atlético Madrid. I mean theory there are favourite of this matches which is Barcelona and Inter. You know Barcelona are having really tough days and Xavi even announced his parting ways with Barcelona this summer. Napoli could make a surprise. Also, Atletico Madrid plays very consistently in Laliga as well as Inter Milan in Serie A, so these two clubs will play carefully, aggressive and defensive, play both of them are equally good.
Barcelona seems to be picking up form as the season progresses. Their biggest problem now is Injuries. So many of their players are out injured. Napoli too seem to be getting better even though they still struggle. I think Barcelona is the favorite for this tie but they have a very little advantage over Napoli.
The more difficult tie is Inter vs Atletico Madrid. Inter Milan is in very good form while Atletico is a very stubborn club that never likes to be beaten by a fellow big team. They love a challenge. They might lose easily to a mid-table team in the league but when it gets to Madrid and Barcelona, they are ready to play their lives out on the pitch to get the win.
I feel like that's how they'll be against Inter in both legs. I honestly do not know who to favor in this tie.
Barcelona is still the favorite to win the Champions League last 16 match against Napoli. In terms of squad, Barcelona has better depth in terms of performance and Barcelona is also better because Barcelona is still at the Big 3 the league while Napoli themselves are having difficulty getting to the top because the inconsistency they have and currently Napoli is ranked 7th which means Barcelona's ranking is much better than Napoli. I don't think many people are favorites for Napoli in this match considering that Barcelona has greater strength than Napoli.
Yes, to be honest, I also can't predict with certainty the match between Inter Milan vs Atetico Madrid because in terms of consistency Inter Milan is superior in the domestic league while Atletico Madrid is not completely consistent but it's not too bad and Atletico Madrid is indeed a club that is quite tough to beat by other top clubs therefore I might skip betting on these two clubs in the Champions League.