what joker is better

Heath Ledger definitely killed it - given the amount of dedication he gave to the role, I'm not super surprised. I remember reading some interviews where the cast said he was constantly in character and he had actually locked himself in a room for a week to get into character.

The newer joker (not the god awful Jared Leto version) from the Joker movie was pretty good and definitely portrayed more of the mental illness side of the Joker.

You also have to tip your hat to Jack Nicholson for his adaptation in the original Batman series as well.