Four beast easily.
Yep, nobody can hurt him. The four beast sliced half a city apart in its weaker form with a simple swing of its arm. Then you have its instant regeneration, multiple limbs, ridiculous strength (far greater than the four kings), ability to learn and adapt to opponents moves and the poisonous green rain. It only lost because Oh Shoku Bansan is ridiculous, and nobody in OP, Bleach or Naruto has a move that's anywhere near close to it. And to think the only reason the four beast is in the human world is because it was too weak to survive in the gourmet world.
@All_StarSupes: it was because of its unbalanced dietthere are no humans in gourmet world. there are flashbacks of the four beast fighting against an adult battle wolf, mother snake and an emperor crow so it is powerful enough to survive in the gourmet world. think of it, you think the asura tiger is stronger than the four beast? no way.
To be honest I'll say the four beasts could pretty much solo the majority if not all of OP, Naruto and Bleach combined.
I disagree, those series are still going on and haven't show all of there moat powerful characters yet (really dislike people when they say someone could solo a verse)
Also One Piece, Naruto and Bleach if combined, they will destroy it fairy easy with there most powerful characters
Back on topic: 10 tails isn't in his final form yet, so Four beast win by default until it goes final form and see it true power