Simmons would be #1 based on potential, he's unpolished, but come on, how many 6'10 240 guys (and he'll probably max out close to 6'11 250 when he grows up) have that kind of athleticism and court vision? You can teach a jump shot if a player wants to work (see Leonard, et al), and defensive positioning, but you can't teach spatial awareness, size and athleticism.
It's easier to coach up a great athlete (though risky) than to get a polished college player to play above his athleticism in the NBA, or why so many college stars are meh at the next level.
My theory of drafting is go for a combination of athleticism and intangibles (work ethic and compete level) early, athleticism later, and polished but limited athletes who fit bench roles in the late 1st and early 2nd rounds - and European stashes in the 2nd round as lottery tickets (given them a few years to surprise using low value picks).