Saric or Smart. Both are "winners" that could be plugged in and given real minutes from day 1. Each would work well in Stevens's motion, 2 point offense (Smart as a 2nd PG and Saric as a point forward). Both have enormous, all-star upside. Both have high BB IQ and a strong desire to win. Both can contribute to team defense, though Smart has higher upside as a defender. Saric has higher upside as a scorer and rebounder. Saric's performance in the Adriatic final 4 was ridiculous.
I don't think #6 is any worse than #5 in this draft, especially since Randle is very likely to go top 5 and the Celtics were unlikely to take him.