Jason Todd
He might not be everyone’s first choice due to his history, but there’s been a noticeable change in Jason Todd’s demeanor over the past few years. No longer is he the coldblooded vigilante of before, as he now acts more in the mold of the Bat.
He’s undoubtedly the angriest member of the Bat Family, but he’s also the one who cherishes what Bruce has done for him the most. If something were to happen to Bruce, for example, it could either send him off the deep end or inspire him to be everything that his mentor thought he could be.
Despite all that’s happened, Bruce hasn’t given up on Jason. He sees something in him that the rest of us have obviously missed. Perhaps Jason could still be the heir to the Bat throne. Just don’t put him in a room with the Joker, though, because then he’ll break the ‘no killing’ rule in a heartbeat.