It's Embiid by far. He is:
-the best defender right now
-the second best scorer right now, behind Parker
-the biggest potential star, as he went from total nobody to college superstar in just one year.
Obviously you listen to the doctor, but it's not like the other guys don't have issues:
-Exum hasn't faced the highest level of competition yet, so it's hard to evaluate his defense and his ability to finish vs elite rim protection
-If Parker fails to improve his defensive effort, he will be the constant iso target of opposing team's game plans
-Wiggins doesn't just lack polish-- he lacks offensive skill. Poor handles, poor touch at the rim, poor physicality to finish through contact. Average shooting, average passing. He put together decent scoring totals by virtue of his great athleticism, but his efficiency has been far lower than his teammate Embiid's, despite the fact that opposing teams constantly doubled Embiid in the post. The biggest issue with Wiggins is that he will struggle to adjust to the physicality of the NBA, as his strength and apparent lack of aggression makes him a poor finisher through contact against much lesser collegiate rim protectors.