This isn't so much about who acted the better part, but more so who was the better villain as a character.
It's a toss up. Joker is incredibly entertaining to watch, while he enacts chaos. However, Bane gives me chills and goosebumps whenever he's on screen, he's that much of a presence.
So, who was the better of the two? Who had a more villanious and malicious impact on the story? Who, overall, had the largest screen presence as a villain, I suppose.