Yes you are right it is hard to know which team will be best in Serie A next season. Teams like Napoli and Inter Milan have had good and bad years. Now many top teams have new coaches which makes it even harder to predict. But we know that Napoli hiring Conte is big deal. He is great coach who has won many championships in Serie A. I also think he will make Napoli strong team again and maybe even lead them to another championship. He is good at motivating players and making smart decisions so I would not be surprised if Napoli does very well next season.
One very enjoyable fact about the serie A is that you cannot see any long stretch of dominance by any team, it's mostly that teams just gets to have this dominance awhile after which another team takes over the dominance awhile again and the rotation continues. This new season where it appears like all of the teams are putting in great efforts to getting better could aswell mean we expecting a very good and interesting season at the serie A where we are going to see teams battling the top position on the table again, the title race obviously is going to be fierce than it has been in previous seasons.