It depends on the type of fight.
Sea serpent, dumb beast, would obviously only be dangerous if one was stuck in the water on a smallish boat( or a large one and caught unaware), in such circumstances, however, I wouldn't want to cross it.
Maugrim would be most dangerous if I were in a position where survival depended on outrunning or otherwise hiding from a massive wolf.
Whilst not terribly formidable in any other arena, I wouldn't want to engage in a physical battle with either Miraz or Radabash. They're both also pretty cunning and manipulative, but I think their true strength lies in the common means of combat.
Jadis, certainly a dangerous witch, to me undoubtedly stronger than the Green Lady, and, as a witch, more powerful than the more physical fighters, seems to be the one I would least want to fight, in general.