That really depends. Ohtani the pitcher has an average draft spot of 77.6 while the hitter is ranked much lower. The immediate problem with Ohtani as a hitter is whether he'll get the number of necessary at-bats to be worth a roster spot. If you can get Ohtani with a relatively late pick (outside the top 200), he could be worth a flier as long as you have position flexibility elsewhere.
Ohtani the pitcher is much more interesting. That being said, it's tough spending a top 100 pick on a player who will probably face an early adjustment period to facing big league hitters. For that reason, I'd probably pass on him in Yahoo formats. ESPN's ranking of 103 seems more right for the DH/SP.