Serie A will be the best option for him, moving to the league he was once comfortable at before his move to Man United and at Napoli he has a better chance of medal and improvement under the management of Antonio Conte than under his former coach at United who signed him but couldn't bring the best out of his signing. While Bundesliga is not really tasking in compare to the EPL moving back to Serie A is better for him.
Playing under Ten Hag didn't allow Rasmus Hojlund to develop, and that's the same as staying at Manchester United. Therefore, playing for Napoli is better than moving to Leverkusen, as he has a greater chance of success in Serie A. Furthermore, he understands Serie A better than the Bundesliga, making it easier for Rasmus Hojlund to improve his performance. The problem now lies in the transfer fee, as Manchester United are unlikely to let him go cheaply, making it difficult for Napoli to acquire Rasmus Hojlund.