Originally I was thinking Saric, but looking at this list here and the numbers, Brogdon's FG%, 3pt FG%, AST, STL, and being just behind in points makes it tough not to lean towards him, just with a quick glance at numbers. 46/41/86 splits is impressive in relation to Saric's 41/32/79. Of course Saric's got him in rebounding though, and slighly in ppg.
http://basketball.realgm.com/nba/stats?rookies=I haven't watched either enough to know their entire impact defensively etc, though, and of course these are just raw #s and I haven't looked at any advanced data.
It's really too bad Embiid didn't play the whole season, because he probably would have been one of the better rookies in quite some time. Once that team comes together, and if Simmons lives up to the hype, they will be interesting, particularly after likely adding a guard or two at the top of the draft.