Ben Simmons looks like a great regular season player, that will put up nice stats on bad teams. His poor shooting mechanics may be difficult to correct at this point. For a player who handles the ball so much, he also needs to improve his free throw shooting too.
Brown seems more like a player that teams would want during the playoffs, since he shows the desire to defend and can hit the open 3. His ability to take it to the rim is also improving.
The thing going for Simmons right now, is that he still has that mystery of being a consensus number 1 overall pick, especially since he missed all of last season. With Brown, we have a year already of seeing him play as a rookie and are more aware of is flaws. We are just starting to see Simmons play now and becoming aware of his flaws. They also have very different roles on their respective teams. Philly gave Simmons the keys and wants him to be their star player. Brown is being asked to play a role on a potential Eastern conference championship caliber team. If Brown was on a bad team like Philadelphia, then I'm sure he would be putting up really good numbers too. I see Brown as being a better scorer and defender, while Simmons is easily the better dribbler, passer, and rebounder.