Well Philly will surely not going to keep all three centers, so they could trade either one of them, they will decide. All three of them have some risks with them. Embiid is a huge injury risk, without single minute played in the NBA. Okafor showed potential but as someone already said, there is no guarantee he will be abe to play decent defense. Also there is character issues with him.
Of all three, the most player I like is Noel. He's prototype of modern center, very agile, real rim protector, can guard multiple positions, but there are legit injury risks wit him also. He's a hometown kid and I would be very excited if we could trade for him. Maybe him and Covington for our bkn pick...