New legit = will jump big either into league top 100 lists, or the team's top ~5 rankings. Can currently be in the top 10 if you think they will jump into 100 list considerations. Can even jump to MLB. Basically, achieves blue chip prospect status.
Sleeper = currently outside team top 15 or 20, will jump into team top 10. Or jump into an MLB role (ex. Girodo)
Really it's just sleeper and deep sleeper.