I will put my money on Napoli to win, if I must, in that game. AC Milan is in top form now, but I don't think they will be able to beat Napoli. Most teams have not really faced a tough opponent, but Napoli performs better against tough opponents. Milan is inconsistent, and that might play against them this weekend.
AC Milan has an advantage of not playing in Europe, so they don't need to reserve any players. Plus, they will be playing at home, so they can use that to their advantage, but still, I'll bet on Napoli.
If you want to play it safe, I think an under 3.5 goals will not be a bad option. Neither teams concede much. They might not want to attack too much, so the opponent doesn't exploit their defence. I've not checked it to see the odds, but if it's reasonable, I'll bet on it.
The feature is tricky. Obviously, Napoli is the stronger side, but I won't be quick to give them a win. It won't be easy to win at the San Siro. Last season, they won AC Milan at the San Siro, but I'm sure they can do it this time around. After AC Milan's shocking home defeat on matchday one, they've bounced back and are on a three match winning streak. So it's kind of difficult for me to give Napoli a win, but over 2.5 goals looks feasible.
AC Milan do make sure they show no signs of weakness at home so I can agree to them been able to really making it tough for Napoli but Napoli on the other hand will fight hard because they are looking at the league title this season so basically we should expect less goals but more performance from both sides since it looks like they both have something at stake.