SS Andrelton Simmons
Not the prototypical build-around player, but there is a pretty huge shortage of productive young position players and shortstops in MLB right now, and Simmons is both. He doesn't turn 25 until September and last year he was worth 4.7 WAR despite a .247 babip. Most of his value comes from being a generational defensive talent -- last year he saved 41 runs according to Fielding Bible, which was the highest score of any player in years. A shortstop that incredible defensively doesn't need to hit much to be valuable, but Simmons has also shown signs of improvement at the plate, including hitting 17 HRs last year. His bat doesn't need to get much better for him to be a star, and if it improves a lot he's one of the best players in this draft.