I would bet Atalanta to win straight away, Atalanta is just too strong in this season. Milan showed if they're getting better, but they didn't win against Juventus and Napoli, so they're still struggle to fight against strong teams.
BTTS is likely to happen, but over 2.5 goals is quite risky, if you check their head to head, the results are mostly 2 goals.
I agree about Atalanta. They are just rolling not only in the Serie A but also the Champions League.

This is why I don't have the courage to go double chance on Milan.
Actually the last head-to-head at Atalanta's home ended by their 3-2 win against Milan. Maybe we might see another similar result who knows...
While Napoli and Atalanta have tough games ahead this week, it might be a chance for Inter to get nearer them in the standings. Inter are hosting Parma tomorrow and I don't expect any surprises.