Despite the roster jam, I'd take Ball. He's the consummate team player and most unique talent. A 6'6" point guard who would be near the league lead in assists, score efficiently, rebound, defend, plus ball-handler, no character concerns.
Futz may be more explosive offensively, but he's not on the same level of passing or efficiency, and Ball has a solid 2+ inches on him.
Obviously I'd be happy with either, of course. Bradley would probably be the odd man out when he wants his monster contract, and would be trade bait for a big man.
Theoretically I want the best big man available, but I just don't see one in the same league as these guys yet.
Thomas / Ball / Smart / Rozier / Jackson (guards)
Crowder / Brown (swings)
Horford / Zizic / Yabusele (bigs)
Bradley: trade bait for another big
$$$: max free agent