As probably the biggest Anderson fan around, I think Williams is better pass rusher and if the Ravens want an immediate impact off the edge, they should take one of Williams/Harris/McKinley with their 1st round.
Overall, I'm repeating myself I know, Anderson is just a complete player - he does everything very well as a 34 OLB and his biggest asset is his football intelligence. He diagnoses offense really well and you'll almost never find him out of play. Maybe Ozzie can find a way of taking Anderson without spending 16th on him?