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.
For me, Inter are not favorites even though maybe you only consider their position in their respective league standings but yes, I still favor Atletico to win. But regarding Barcelona I think it is clear, at least Barcelona still has a more experienced and better squad compared to Napoli's squad. So, even though at this moment Barcelona and Napoli are not in a good trend but still, basically Barcelona is still a team that deserves to be favored to win and advance to the quarter-finals compared to Napoli. Because after all, Napoli's problems are not only about declining performance this season, because Napoli has problems regarding the new coach and also about the squad which is not completely good. Therefore, I believe Barcelona will still have a very good chance of beating Napoli later.
Everyone having his own views and statics about coming matches with few are going with group stages matches performance as well, but currently we can't give perfect predictions about any team with UEFA Champions League is mostly having performance which happen on match day better results many times we have winning teams which were not in frame of win but still they achieve their targets and having winning matches and trophies as well.
Here I agree about Barcelona vs Napoli with most chances we will have Barcelona better and experienced team and can win against struggling Napoli which is having worst season but about Inter Milan vs Atlético Madrid I am sure it's going to be one of the interesting matches in this round with any team can win, and I have personal view both will win their home matches, and we will have winner from penalties which will be luck game.