Merlin, most of the time. The man walks onto a battlefield, ignores the complete carnage, and asks for volunteers to help find the magical cauldron. Also, aside from Cerdic, everyone is downright terrified of him at one point or another. Especially Mordred, who had previously seen him as a tired old man who likes cats. This impression is crushed when Merlin threatens to turn him into a toad and frightens him into giving him [Merlin] the necessary information.
Also when Merlin wakes up after finding the cauldron and asking for cheese.
Sagramour is a walking CMoA. At one point, when an alliance with Cerdic, a notoriously treacherous Saxon king is proposed by a Prince who seems to permanently hold the Idiot Ball, he states that he will not make peace with Cerdic. When the Prince tries again, he delivers a Death Glare and repeats the same thing, as if talking to a child.
Near the very end of the series, Culhwch gets a truly awesome moment. He walks out in between two armies who are facing off and challenges anyone from the enemy army to make a name for themselves by killing him in one-on-one combat. When no one takes him up on it, he taunts the entire army about their cowardice in refusing to fight an old man. As he turns his back, one spearman does try to backstab him, but Culhwch effortlessly guts the poor bastard, waits a few minutes to see if anyone else wants to give it a try, then returns to his place in the shield wall. Awesome.
Derfel has had his fair share and then some. He has some notable victories is duels, which include very cleverly utilizing his shield as a thrown weapon and defeating the Saxon champion and professional duelist Liofa by breaking Liofa's sword. Then there are other ones too like managing to rescue Nimue from the Isle of the Dead, and so on.