The first was screen actor Cesar Romero. He played the character like a whimsical foil for the man in tights and his cornball sidekick, Robin. His character never seemed as evil but more so a carnival games director that had a penchant for trickery and avoidance.
Secondly, the Joker returned to film in the 1989 Tim Burton film, Batman. This is considered by some to be their favorite incarnation of the character. Jack Nicholson played the role with a more sinister style. The laugh more evil and a plan more malevolent added a certain dynamic to this new take on a classic character.
The third and latest portrayal was by (of course) Heath Ledger. Ledger added his own touch to this representation of The Joker. Stylistically like a mix between The Crow and a mad man armed with masquerade masks, Ledger's style defined how most people will perceive The Joker for years. This time, he had a desire for anarchy and destruction. Nolan and Ledger modernized the character while making him more ambitious and quite lethal.
I've experienced all three characters and can honestly not decide which I've liked best. While I could easily pick Ledger, it's not that simple. I feel that each actor has truly lent their own personality to each portrayal.