I would rather build around Davis, but Okafor could be special. He has already improved quite a bit during this season. I watched the Duke/BC game and was totally impressed. His last 3 games he has gone for 27, 24, and 28 on better than 75% shooting. His fundamentals are reminiscent of Duncan, but he's not as athletic or as good of a defender.
After Davis, I'd go with Okafor as far as young big men. Embiid has more upside, but he's a project and already has a worrying injury history. Drummond is the better defender and rebounder, but I'd rather have Okafor's post game. Cousins is too much of a hot head.