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.
Of the four clubs you mentioned, perhaps only Barcelona has a negative performance trend in the domestic league. It is likely that Barcelona will not be the favorite even though it is a big team. Because he remembered that Xavi had difficulties in several previous matches.
Napoli and Atletico Madrid have almost the same chances because both of them can be said to be not bad in the domestic league. Even so, there are always surprises that occur in the Champions League. Because the battle for prestige of all participating clubs will affect the overall playing mentality.