Heinrich. Warren and Brown are great at alienating people, Castro's experience level is very low, and Kaine is the definition of an empty suit. Heinrich has the best personality for a running-mate of all five, besides the regional balance.
Kaine has been getting a lot of hate on Atlas lately because people like to root against the top dog or don't just want to go with what everyone else is saying.
He's not an empty suit. Kaine is a smart, accomplished, well-liked and reasonable guy. He'd make a perfectly good VP or president.
Castro is an empty suit. Unlike Kaine he's never done anything of note.