Gee I sure do wonder. No idea who that could possibly be.

Joker

As much as I hate to admit it, Joker.

Personally, I believe Bane or Ra's al Ghul should be Batman's nemesis.

Joker or Deathstroke.

Who broke the Bat and who killed Alfred again?

The good old ... himself.

Nope. JK, obviously the Joker.