Bruce Tim would be a great choice. He obviously have much love for the characters and can translate them from comics to a larger audience.
MoS is definitely the canary in the coalmine. IMO, it doesn't look like much the build a "universe" on, but if it's a hit, there will be a sequel, and it would be foolish if the focus of that sequel was "more Superman" rather than building a cinematic DCU.
That said, I don't think WB's goal should be building towards a JLA movie per se. WB should view its DC properties as almost the opposite of the Marvel approach. Instead of launching a bunch of solo movies to build to a big team-up, WB should roll-out with team-up movies that can spawn solo movies. Reboot a Batman series through a "World's Finest" sequel to MoS, and just keep adding heroes to the main vain of DCU movies and spin-off from there.