Christian Bale because he's the best one, obviously.
On a slightly more serious explanation, he captured the brooding and pain that was in Keaton, but he also brought a nobility and a true sense of purpose to Bruce. You could see his pain and anger in the eyes, and even the boy in his face even as it aged, but you also got a sense of passion and genuine affection for his city... and how he would do anything to save it and his parents' legacy.
Plus, I liked how he approached being Batman on a macro level of cleaning up the city and really using Batman as almost a political campaign, and enlisting trusted people to help build its shadow across the city. While less pure comics where "the mission will never end," it actually shows a cunning to Bruce as he does not approach crime by merely attacking the symptom (rich guy beating up poor people). He is trying to clean the city up economically and ethically, so as there not to be the environment to breed more crime.
Keaton's Bruce was more anti-social and damaged, and just doing it to satiate his own demons. And Affleck's Batman is just a raging *******. He kills like Keaton, but unlike Keaton, there is kind of a sadistic joy about it, and he has that obnoxious Ayn Rand "might makes right" fascist crap that Miller and Snyder drool over. He also doesn't view it as making the world a better place, it's about proving his manhood and... screw that interpretation. The only way to salvage the Affleck Batman is to have a page one rewrite once Matt Reeves comes onboard. Even then though, he lacks the presence and nuance of Keaton or Bale in the role.