As a psychological thriller, exploring the depths of human experience and the origins of Bruce Wayne's transformation from billionaire playboy to protector of the people, I have to say that "Batman Begins" has the edge over "Dark Knight."
With Wayne's deeper and darker motivations already established, "Knight" continues the exploration of his temptation to turn to the dark side, led into this valley of temptation by his own personal emissary from Satan, The Joker. Christian Bale's performance is outstanding but Heath Ledger's "Joker" , just as everyone has already heard, steals the show. In fact, Ledger's performance steals the show from every film I have seen this year.
Despite the Academy's reluctance to give an Oscar to a deceased actor, I don't see how they can possibly avoid it. An okay actor (Sorry, the buzz around Brokeback was mere titillation; the acting was good but not exceptional.), Ledger delivered the performance of a lifetime. Had he lived another 60 years, I doubt he could have replicated this one.