I think it's hard to pick Long because he's entering year 4 and, really, how many guys make big leaps forward from years 3 to 4? Not many. Not that he won't contribute as one of their top 4 CBs. I like Scott a lot but think he will pick up where he left off.
So I pick Rochell. He had the most meaningful snaps (234 on defense, 7 games with at least 14 snaps). He had the look of a guy that "belonged" right away and to me is exactly the profile of a guy that takes a big step forward in year 2.
I remain somewhat skeptical of Blanton and Hopkins. I really hope one or both pleasantly surprise me.