Smart: Made All-Rookie 2nd-team (garnering the most votes of any 2nd-team player), Celtics starter during their playoff push and brief playoff existence, starter and defensive anchor for defensively elite 2015-16 Celtics. Age: 21 y.o. Weaknesses: wildly inconsistent offense. Can put up nearly 30 on Russ only to shoot 1-11 against Ty Lawson and James Harden. Biggest question: Can he gain some consistency to his offensive game and average 15 ppg? Runner-up: What guard spot will he succeed best at, and will he necessitate acquiring a backcourt partner that fits uniquely with his game?
Mudiay: Starting and producing for a better-than-expected Nuggets team. Can really score and get to the line, has a respectable jumpshot for a non-jumpshooting rookie, can create for others offensively, has the size and agility to be a defensive playmaker as well. Age: 19 y.o. (almost exactly 2 years younger than Smart). Weaknesses: jumpshot, turnovers, defense. Biggest question: Can he become a respectable long-range jumpshooter? Runner-up: Can he use his physical tools to become a good-to-great defender?
I would expect the answer to this question would be totally different if I asked it after Smart's 26-point outburst against OKC -- or even his dominant defensive showing against Houston -- rather than after a couple of bad games in a row (DAL, BKN) and a subsequent injury.
My answer is Mudiay. He's younger and has less severe issues on any one side of the ball. Smart looks like a legitimate defensive anchor at the guard position, but his offense at 21 in his second season is more concerning than Mudiay's defense is at 19 in his rookie season. Perhaps if Smart was given the offensive liberty over the past 100 or so games that Mudiay has had in his rookie season, we'd have already seen a lot more offensive "flashes" from Smart, like in OKC.
Know this, though: Smart's defense is more impressive than anything Mudiay has shown at the NBA level thus far. If Smart can ever cobble together 15-18 ppg, 5-6 rpg and 4-5 apg to go along with perennial DPOY candidate-level defense, he will go to the All-Star game multiple times and be a legitimate 2nd or 3rd banana on a championship team.