This is tough, the dog with the garlic clove on his nose clearly has discipline. The dog wearing the hat as a tortoise shell has the crazy eyes you don't want to mess with. The Corgy looks fierce. The dog with the bananas is the biggest. I don't know about dogs, but bananas are a good food for humans after a tough workout (or fight), not before.
Reexamining this. The upper left dog might be a contender but I'm going with the lower right as my champion. The upper right dog has crazy eyes, but in my experience, crazy dogs tend to be cowardly and skittish rather than fighters. The lower left dog is in battle gear, but battle gear doesn't matter in real dog fights, and it's a corgy. Corgy are too adorable to be a threat and whatever fierceness it's displaying is probably really discomfort at the stupid thing on it's head that it wants to shake off. The lower right dog is big and it seems neutral when it comes to vibes. The upper left dog is smaller, but I sense it is scrappy. I would name it the number two slotted dog.