The "gold" standard: Comic books have fairly old roots in pulp fiction. DC Comics is short for "Detective Comics", which should give some strong hints as to that origin. Even Spider-Man (yes, this is how Stan Lee originally spelled it) was originally written in the old pulp detective style. If you read the origin stories for both, and then compare them to "true crime" rags still written today, the comparison should be obvious. Yes, granted, the "true crime" genre has been subsetted and even supplanted somewhat by the "true romance" genre, but both have common roots.
Contender #1: Adam West
I shouldn't have to explain to children of the 1960's about '60s Impressionism or anything like that. But I will speak to comic books of the period, because not everyone might be well familiar with that. Please be merciful with me as I was not born then and speak as an outsider.
Comic books were still printed in the four-color format, and the Comic Book Code was adopted to quell the conservative backlash against comic book's so-called "unsavory" image at the time. In other words, it was a set of standards of what comic books could and could not publish in order to receive the seal of approval.
Batman was reinterpreted as a father figure, in much the same way that Superman was (although he, too, was not originally written this way). The whole era of sidekick companions was also introduced (e.g., Robin, The Boy Wonder) as to complete the whole "father figure" and "aspiring young son, not yet a man" theme.
So the Batman TV show and subsequently Adam West's portrayal of Batman was heavily influenced by this whole "young boy comic book reader, here are the heroes you should emulate" Golden Age "four-color" comic book style. It was as melodramatic and exaggerated as the comic book was. It should be noted that he replaced Olan Soule as the voice of Batman in cartoons of the late '60s and '70s.
Contender #2: Michael Keaton
As I told ms. emily sears, I personally thought Michael Keaton made a fairly lousy Bruce Wayne, as he has had more "Joker"-like roles during this time period, and it is difficult to separate him from that and take him seriously as Bruce Wayne. Maybe I have no clue what a billionaire playboy should be, maybe aside from Sir Thomas Branson, but I did not like his portrayal of Bruce Wayne.
However, I thought his performance as Batman in the first film was more noteworthy. Although the critics were drooling over Jack Nicholson's ad-libbed lines and overall performance as The Joker, I disagreed with the estimation that Keaton's Batman was less than a perfect foil for the Joker, or vice versa, depending on how you look at it. They were very yin and yang, one being tall, dark, and silent, and one being short, colorful, and loud.
The second film was worse, in my opinion. Any respect I had for Keaton's Bruce Wayne vanished as Batman tore off his cowl, revealing his identity to Michelle Pfieffer's Serena/Catwoman. Some of you fangirls might think that a romantic flourish, but I thought "You idiot, what the hell are you doing? You're exposing yourself to a villaness– a wild card at best!"
Contender #3: Val Kilmer
Good Batman, very very lousy Bruce Wayne. I generally don't agree with Joel Schumacher's gay interpretation of Batman, but Val Kilmer seemed to manage fine in some aspects.
Yes, I am aware Kilmer player crazy guys, too, from "Real Genius" and such, but I think since he was a little better at a serious face, I thought he was a little better at Batman. The Bat gizmos were starting to come along nicely before looking like fad gadgets by the time George Clooney took the helm.
Kilmer is not a natural blonde, so why was his Bruce Wayne toeheaded? Something else to shoot Joel Schumacher over. He just didn't have the presence I felt he should have, besides Bruce Wayne NOT having golden hair.
Contender #4: George Clooney
Excellent Bruce Wayne, abysmally bad Batman. I shouldn't have to explain the train wreck that "Batman and Robin" was, either. When George Clooney said "Howdy, [Mr.] Freeze, I'm Batman", I just wilted inside. Batman does not say "Howdy". He played Batman much too casually, in my honest opinion.
I thought his Bruce Wayne was comparatively better. Clooney is much more able to pull off that Gentleman's Quarterly look, and that's pretty much all I need to say about that. I will admit that he was lacking grit, however, but that affects both the performance of Bruce Wayne *and* Batman.
Overall, George Clooney went down with the short-lived demise of the Batman franchise. Although his Bruce Wayne was very, very good in some ways, his cosmically bad performance as Batman overshadows any of that.
Contender #5: Christian Bale (current challenger)
I have yet to see The Dark Knight, but I rather enjoyed Batman Begins. I think he better captured the angst of the original 1930's Bruce Wayne. His performance of Batman, however, seemed to be a bit lacking, but my opinion may change once I am able to see the newest film. His gravelly Batman voice seems a little contrived at the moment, and his Batman persona is not omnious enough yet, in my opinion.
Honorable Mention: Kevin Conroy
Kevin Conroy is known as the current voice of Batman, and I hate to give him an "Honorable Mention", because, frankly, I think he's the best voice of Batman, period. In an ideal world, all the other actors should have had a voice more like his, even if it has to be done post-production with voice synthesizers and other studio wizardry.
Wikipedia states he has portrayed Batman more times than any of the aforementioned actors, combined:
"In a tally of performances that include every episode, movie, and guest appearance made as the voice of Batman, Conroy has played the character more than Adam West, Michael Keaton, Val Kilmer, George Clooney, and Christian Bale combined."