His lack of aggression was due to his team's poor play I think, he admitted to getting down when the team wasn't competing, and got benched for it. His physical skills are fantastic though, and on a winning squad, I think he'll be fine. He has the best hips in the draft.
Hall I think will be a better safety, he struggles against top receivers for a reason, namely his lack of burst and explosion. Merriweather is awesome, one of my favorite guys in the draft, but the head stomping thing worries me. Not that he'll be Pacman Jones off the field, but that he'll lose his cool and pick up stupid penalties and give up big plays by being overaggressive. On pure skill though, he might be the best safety in the draft, with his ability to slide over and cover like a corner, in the slot or outside. Davis is too slow to be a top guy, but he might make a decent slot corner.