I don’t see a need to choose between Brown and Hayward at all.
Me neither. Even if there would have to be made a tough decision, it's probably more likely that Hayward and Tatum come in each other's way. Since for both it seems that SF is their single best position.
But I'd like to hear some arguments by the OP why he believes that there has to be made a choice between Hayward and Brown. Other then the observation that the starting line-up at the beginning of the season that included both Brown and Hayward didn't work out and that the players need time to adjust to find their roles within the team, what arguments are there why specifically Gordon Hayward and Jaylen Brown couldn't both stay on the team and be succesfull?
What is the reasoning behind starting this topic?