Boston is the only team that already has a playmaking high scoring all star. Hayward is a smart dude. He knows that he is not an alpha dog. IT is. He gets to play next to an alpha dog, a guy who will create a lot of bunny jumpers for him, and also gets a max contract. Oh and he gets to play with a coach who was the first person on earth who convinced him he was going to be an NBA player.
If Hayward is strictly making a basketball decision, it will be Boston, and it's not even a close call.