Discuss, discuss.
It's definitely not a Shichibukai chance here, the Shichibukai ISN'T a pirate crew, so don't even try to bring up any marine or Shichibukai inflicted pirate crew… in my opinion it's between... Blackbeard and his crew, Whitebeard and Shanks'....
Why I think Shanks has a kickass bounty?
He wants to go to war against Whitebeard(we actually never knew what happened after tankobon no. 25 between… Whitebeard(the Rockster situation) and Shanks.. maybe they even fought...) and... Edwar D. Newgate is the world's mightiest.