I think one of the most common but inaccurate comparisons is Andre Iguodala. Iggy played point forward for a majority of his career with the Sixers and occupies that role similarly with the GSW. Iggy's passing and handle are his most outstanding offensive features which are two of the biggest knocks against Jaylen right now. If there is one thing holding Jaylen back other than maybe his defensive awareness it would be his ball handling skills. I don't see Jaylen playing the same role that Iggy has for the majority of his career.
NBADraft.com cited Jason Richardson as a comparable player and I can see the similarity in their athleticism and finishing ability. Richardson wasn't quite the ball handler that Iggy is, but he was decent enough and was a strong scorer, good playmaker (not on Iggy's level), and flourished in an uptempo system (i.e., GSW). I can see some similarities.
The most common comparison is Jimmy Butler and I can see it to a certain extent on the offensive end, but I can't envision Jaylen being on his level defensively.
There are some players who have clear cut comparisons (e.g., Tatum/Parker and Carmelo; Ball and Kidd), but I feel that Jaylen is too raw of a prospect to know what we're getting. He has a lot of potential due to his size and athleticism and he does have some strong skills that translate well (e.g., finishing; straight line drives) and some flashes on brilliance that could be mastered (e.g., post-up game; on-ball defense), but as of right now I think it's hard to even project what kind of prospect he is. He could be an all-star or sitting on the bench in ten years.