Hindsight is always 20/20 and I'm saying this with hindsight in mind,
DeMar was clearly the better pro prospect. Had a defined position, had better size for position, and is much more athletic than OJ. OJ got to the NBA primarily being a difficult shot taker and maker. He took those difficult shots because he was too slow and small to beat people off the dribble, relegating him to taking tough shots. That only amplifies playing against the most elite athletes in the world. Even on the amateur ranks, OJ took mostly jumpshots and never was a high volume free throw guy.
Conversely, Demar (Who went to the same HS as my mom. Tarbabes
) had size, scored in a lot more variety of ways, and was / is a supreme athlete. Demar in HS was a monster. 6'7, smash on your head, could post up really well, midrange game crazy, In essence, he had qualities that would allow him to be a much better pro.