Currently there are still three teams that still have the potential to continue competing in terms of the fight for the title in Serie A and that will still make the competition even fiercer until the end of the season. The teams are the ones you mentioned, namely Atalanta, Napoli and also Inter Milan who are currently still leading the Serie A standings. And I still hope that all three can consistently win until the end of the season so that the determination of the Serie A champion this season occurs in the very last match.
Inter Milan is my favorite team to win the Seria A this season because I think they have the best squad in the competition, but we have admit that there are teams that can compete with them even though experience will letter give Inter Milan the upper hand to win the Seria A.
Atalanta and Napoli are the two teams that are close to Inter Milan; Napoli is just three points away from Inter Milan, while Atalanta is almost six points away from Inter Milan, it clearly shows that Napoli is the closest competitor because they also have an experienced manager that have been in the Seria A for long time now.
Napoli will have some advantages over Inter Milan because Inter Milan will be playing in the Champions League, Copa Italia, and the Seria A; while Napoli will only focus on the Seria A matches. Inter players might be tired due to too much matches, while Napoli will have enough time to prepare for their each games which can be of high advantage for them.