Conroy, straight up. I think they're all phenomenal actors, but Conroy's the only one who really seems to understand how the character evolves over the course of his career, thanks to the benefit of the DCAU's ongoing continuity. Specifically, you can hear it in the stark contrast between his Bruce Wayne voice and his Batman voice early in his career, and how they sort of merge over the years. In the early episodes of Batman: The Animated Series, the lines between Bruce and Batman are clearly defined. They sound entirely different, and you could be forgiven for thinking this was Bruce's attempt at maintaining a normal life. As time goes by and we segue into the New Batman/Superman Adventures and Justice League, the Batman persona starts to take over, and by the time we arrive at Justice League Unlimited, there is no Bruce Wayne anymore. Bruce Wayne is an occasional disguise, a mask to use when he needs the legitimacy of Wayne Enterprises. Underneath that mask, he's Batman entirely.
And then we arrive at Batman Beyond, which I think is probably the most interesting portrayal of Bruce to date. Finally too old to continue fighting crime and alienated from everyone who ever cared about him, Bruce pretty much has no reason to live. He's redeemed by Terry McGinnis, a Batman who was born out of tragedy, just as the original was, but also a Batman who manages to rise above it. Terry manages to balance his duties as Batman with making time for his loved ones, and his determination to do so prompts Bruce to do the same, leading him to reconnect with long-lost friends in his twilight years.
There's always the question of how much of this you can contribute to Conroy, and how much belongs to the brilliant writers of the DCAU, but Conroy really knows how to sell it. As far as I'm concerned, he is the Batman. Of course, it doesn't hurt that Conroy's often playing opposite one of the very best Jokers.
