Napoli, especially since they have been able to confirm Conte as manager, are still the best team together with Inter in my opinion. The real question is how Napoli are going to perform this year because they are going to play the Champions League: last year they were playing only one match per week, this year things will change, so they need more depth in the team, they need more players because Conte doesn't do a lot of rotation.
Juventus, Milan and Roma will simply fight for a Champions League spot.
Napoli is one of the most active Serie A teams in the transfer market, tehy seeking to add depth to their squad to cope with the increased workload next season. Napoli's management made a smart move by signing De Bruyne, and Napoli is currently reportedly working on several more new players. This way, Conte will have a team ready to compete in both Serie A and the Champions League next season.
The race for the Scudetto next season will certainly be tougher. Napoli will not only be competing with Inter Milan, but also Juventus, AC Milan, AS Roma, and Atalanta are likely to be in the running. Likewise, in the Champions League, Conte will face an even tougher challenge. Overall, Napoli will have to work twice as hard to cope with the increasingly congested match schedule next season.