I like Thomas quite a bit but it would be more than a bit scary with Sean Smith and Earl Thomas in the same secondary, from a tackling standpoint. Thomas is a willing hitter but with that frame he's going to be a liability in certain situations. I could definitely see opponents game planning to take advantage of that duo's vulnerable tackling, particularly the divisional rivals.
That's the difference with Berry, who is the closest I've seen to Kenny Easley from a physical standpoint, a rangy guy who will also knock your head off. Berry would eliminate concerns that would be front and center with Thomas.