We don't have many developmental players, so I am not expecting any big jump from anyone. Tatum and Brown can still make improvements to their game, but they are small leaps in comparison to where they are now.
I can't go with a rookie who hasn't even started camp yet. I hope he can contribute minutes this season even if they're just energy minutes, but I can't envision a jump when I haven't seen his floor yet.
So that leaves Pritchard, Hauser, the 2 new Bs, and JD Davison. I would like to see a jump from any one of them, because we need role players and shooters that can contribute. Most of them are probably what they are though, so I'm going with JD.
JD Davison was a star at a small time high school, not one of the NBA factories and he probably should have stayed another year in college, but maybe he made the right decision thinking he'd develop faster in the G League than playing another year of NCAA ball. He's got the athletic ability, he just came into the league with skills further behind a lot of the high end prospects. He also has lower expectations placed on him, so he can grow at his own pace instead of being forced into a situation he's not ready for.
If he starts putting it together he has the talent to make a big jump this season.