re: I think everybody that plays The Joker can't not do a very good job

I prefer Nicholson's to Ledger's. Ledger was unpredictable and violent, and liked to pit people against each other to elicit the worst out of them. He wanted to watch the world burn.
Nicholson was a different type of insane, he wasn't watching from a distance, he was already burning and he was going to gleefully burn the rest of the world too.