The both teams are strong but I'd prefer Atalanta to Napoli, to me I don't see Napoli as a strong opponent in this encounter because I see Atalanta as a team that have faced tougher opponent than Napoli and they (Atalanta) did well.
It sounds weird when saying a team at fourth position is stronger than a team at a first position. Possibly Napoli and Atalanta have similar quality but in their early matches in Serie A, Napoli are doing better. In this direct match, perhaps they have quite balancing chance of winning it. Napoli looks to be stronger than Atalanta but not too considerable.
Never underestimate the coach of Napoli, Antonio Conte. This Man has handled lots of high profile matches in the past and has the required experience to navigate his Napoli side to victory against Atalanta. One thing I like about Conte is that, once he has the players he wants in his team, he gives his all to win matches even if his team don't score many goals but 1 goal is enough for him to keep winning matches, and we have seen this Napoli side doing that.
Conte is a winning coach and he is building up a very strong Napoli in his first season with them. Look at how he tightens Napoli defense system with only 5 conceded goals so far, it's very impressive and very abnormal with Napoli style. In many seasons last decade, Napoli are known as one of most attacking teams in Serie A but their defense is never good. Now it is upgrading with Conte and his tactics for Napoli, their defense system is like rock.
Atalanta are playing very well, but they are going to lose their match against Napoli today. And when the time comes for Napoli to play inter Milan they are still not going to lose, either they win again or they will share the points. Conte is a tactician who knows what he is doing. Napoli and Inter Milan are going to win their matches today.
Atalanta with several seasons under Gasperini have been built up very sustainably and their competitiveness is very stable in recent seasons. They have players in and out including star players with important roles in their squad, but over years, Gasperini succeeds to maintain their squad quality and competitiveness. The last season with Europa League title is not like a peak after that they will have downside. As we saw so far in this season Atalanta are playing well and ready to have another successful season.
With Conte, Napoli can beat Atalanta and perhaps this match will not have many goals because Conte will not let Napoli playing too attacking and open their defense for Atalanta.