It's hard to tell, but probably Dark Knight and Batman Returns.

At the end of the day, for its performances and dialogues.
Batman Returns had Danny De Vito, Pfeiffer and The Walken hamming the hell out of Got-ham, and exchanging hilarious, ambiguous quips with each other and Keaton whenever he felt to join in.
It also had lots of Burton-esque surreal magic and eccentricity, like the circus gang or the icy panorama shots.

Dark Knight obviously for Heath Ledger. I like how it creates dilemmas for the characters and asks moral questions, but ultimately, it's done too simplistically, and resolved too easily, all the while beating you over the head with its messages.

Can't say I liked Batman Begins all too much - Katie Holmes was simplistic and patronizing, it relied on rather boring repeated catchphrases like "why do we fall", Qui-gon Jinn was a boring villain... it was just meh.

Bale probably puts up a more versatile performance than in the sequel (especially like the drunk scene), Cilian Murphy is a slick snake, it has atmospheric stuff like Batman's "theatralics" or the hallucination gas... but ultimately... I thought meh.
The character arc was too simplistic and obvious for me to care about.