Durant was a better college prospect imo (and it proved to translate to the NBA). Zion is the easy #1 prospect this draft though, but yeah at 6'7 that's going to hurt in an era where a lot of tall grown men with crazy wingspans patrol the defense. Dude is going to need a more refined game so that he can spread the floor reliably. Whether that be top notch shooting (like Durant) and/or impressive court vision (like Lebron) to open up lanes in order for him to do what he does best and attack. That said, the potential is there.
Regarding Durant:
So far Durant is the only player I've ever seen get a 10 for jumpshot while in college on nbadraft.net:
Kevin Durant | NBADraft.net
Athleticism: 9
Size: 10
Jumpshot: 10
Potential: 10
Ballhandling: 9
"His ability to pull up off the dribble is absolutely illegal for a 6-10 player" - pretty much how every NBA player feels today about dude.
They had his comparison as Dirk Nowitzski/Tracy McGrady and I'll honestly say he's shown to be a hybrid of both in the NBA.