Mitchell has been an absolute stud. I've thought about this recently, here's my take:
Mitchell is the more versatile player at this early stage. In Utah, he has a much larger role than Brown has in Boston, and he's made the most of it. I think he's the more talented of the two, has the physical profile to be a great two-way guy, and is just natural born leader. Talent-wise, his ball-handling and playmaking ability allows him to control the game in a way that Jaylen can't.
If roles were reversed, I think Brown would also be successful but probably less so in a lead role. He's also very talented and still developing, but probably couldn't carry an offense like Mitchell is right now. That said, I'm sure he'd have success anywhere because he's an elite athlete, competitor, smart player, and has made the most of his situation thus far. Perhaps most important, think Brown is the better fit for Boston in his ability to adapt to a more supportive role for now, while also putting up points when needed. He's also the perfect fit for Boston's defensive system built around length and versatility.
Difficult to predict who will be the better player. I can imagine Mitchell will put up better numbers, but Jaylen is also asked to play a much different role and will probably win a lot more in Boston. Anywho, really happy with Jaylen and pleasantly surprised by his trajectory thus far. And enjoy watching Mitchell play.