I think it will be Simmons and Dunn battling for ROY, with Hield having an outside chance too.
I think Simmons is going to put up close to Towns' level of production, with averages upwards of 16/10/3 - especially given that he's playing on the 76ers.
Dunn could average 17/6/4 in his rookie season - I personally think he's a better overall player then Wiggins was when he entered the league, and I think he's a better overall prospect too. One thing is for sure. With Dunn/Lavine/Wiggins/Towns on the floor, you'll be looking at perhaps the most athletic team in the NBA - they are going to run a LOT, and I expect they're going to be much improved compared to last year since they can now establish an identity as a transition team and really use that to their advantage.
I also wouldn't underestimate Hield. He should get plenty of touches in New Orleans, and with Jrue Holiday and Tyreke Evans there won't be a lot of pressure on him to handle the ball or function as a playmaker - all he'll have to worry about is scoring, which is something he's very capable of. He could surprise a lot of people this year and put up some BIG numbers.
As for Brown - I don't know what to expect to be honest. With the contract status of Turner, Sully, Jerebko, Amir and Zeller all up in the air, boston currently has a LOT of minutes to go around at the PF and SF spots. Crowder and Brown are both capable of playign PF in small ball lineups, if Danny doesn't find a starting caliber PF in the FA market then Brown might get a lot of playing time. He should be able to slash, defend and rebound at a high level from day one - whether or not he can hit his outside shot as a decent rate could be the determining factor in whether he has a standout rookie year, or a Michael-Kidd Gilchrist rookie year.
I do think Brown is a much better shooter then MKG was.