I thought Ra's for a while, because he knew Batman's identity and had an entire league of hundreds of stealthy, martial artists assassins that obeyed his every command. The power he controls is massive and extends to all parts of the world. There is also him being essentially immortal. But seeing how joker knows Batman's identity now and is also supposedly immortal, I'd have to give it to joker, if not call it a tie. Joker really seems to be able to do whatever the heck he wants to in the new 52. He wanted to kidnap the bat family and batman and he did it. He wanted to poison and mind control the justice league and he did it. He wanted to drug all of gotham, and he did it. There's not much he hasn't been able to do.

New 52 Riddler, Talia, and 90s Bane would be next, in some order.

Ra's

Before I would say Ra's, but because of Endgame I now say Joker

New52...Hush-Batman Eternal:::Joker-EndGame:::Talia Ghoul-Batman Incorporared:::::Riddler-Batman Year One::::Lincoln March-Court Of Owls

Ra is the obvious answer for clear reasons...As of New52 these are the most dangerous

Two-Face is no where to be found, of course. XD

I don't know, I voted for Joker personally, but I think everyone of these villains have been his most dangerous villain at one point in his long history. They've all had their really good moments, and have come close to defeating Batman.

Physically, it's Clayface, Bane, and Ivy IMO. But Ra's or Joker are probably the biggest threat to both Batman and Bruce Wayne.