I agree that Millsap's position is more of a need than Hayward's. But Hayward is the better player. I think the better route to go is to go for the best players possible, then build a team around them.
As much as I love this current group of players on the Cs, one has to seriously contemplate how different this team might be next year if the Cs draft Fultz and sign Hayward, and depending on IT's injury.
Core: Fultz, Hayward, Horford.
Near core (but probably tradeable): Brown, IT (depending on injury), perhaps Smart
Tradeable assets: AB, Crowder, Rozier
Probably gone with nothing in return: KO, Amir, Jerebko, Mikey, Green, Young, Zeller
I think Smart is the interesting one to think about. He's got value, but is probably one of these guys that has more value playing on the Cs than elsewhere, meaning he'll probably stick around.