They're both very young. So far, GG is the more dynamic scorer with more self-creation potential. His appeal is his handle and fairly advanced body control for a player his size. GG is a raw 18 y.o. with high upside. If he hits, GG has All Star potential, imo. He's at a stage in his career where for the first time he's encountering some resistance and has to put in some work to get buckets. He's got a big learning and development curve ahead of him.
Taylor Hendricks is likely a safer pick, since he can step right into a complementary, 3D role. However, Hendricks looks like he'll need someone else to get him an open look or an open lane to score effectively. Hendricks also defends, which GG seems to do only some of the time.
In a vaccuum, I'd take GG because I really only care about upside. For the Jazz though, who may have a timeline they'd like to hit and who already have a big All Star scoring wing, I could see it going either way.