I'm partial to CB's who can run a sub 4.5, jump thru the roof, high point the ball and stick their nose into the action. Starting with this as a "base line", the hope is that these guys can be coached to break aggressively on the ball, turn & go, look back for the deep ball etc.
Until a few years ago, it seemed as though we kept bringing in "steady Eddie" types who were a step slow, were OK (though not sensational) tacklers whose role was "not to suck." Most of these guys were #2 to a shutdown star at the other corner (like Aeneas) - & these #2 guys got regularly picked on.
The Littany: Massie, Hunter, ToasTito, Knight, Marshall, Gay.
Then there seemed to be a change in the QB's we brought in - more athletic guys like DRC, Jefferson and Toler. (& although he's a safety, Bethel fits the same mode).
Ideally, this should mean that, paired with PP21 will be a similarly talented corner that can't be effectively exploited.
I think we brought in Fleming as more of a #3 or #4 role playing corner to match up with bigger, more physical wideouts. (The other role player designed to match up with smaller, quicker slot guys was Money Mike).
Problem was that - due to departure of DRC and Jefferson and the injury to Toler, we were forced to make Gay (& to a minor extent, Fleming) our #2 corner, and IMO, this became our most vulnerable position on defense.
I hope Toler returns as a Cardinal. If he doesn't, we've got a problem at #2 CB.