I mentioned in the Checking the “Bears Box” Draft Profile: G/C that defensive backs were universally thought of as the most difficult position to scout. While safety is more difficult because the players are generally off the screen for most of the play, cornerback is worse for me.
In the most general sense, safeties can usually tackle better than cornerbacks. This makes stomaching their play a little easier. College cornerbacks on the other hand generally do not possess the requisite toughness to play football at the NFL in my opinion.