I'll nominate two swordsmen.
1: Ser Arthur Dayne, The Sword of the Morning: This man is a legend, pure and simple. One of the last true Knights of the Kingsguard and considered that most dangerous of the 7 (which at the time included both Barristan Selmy and Jamie Lannister), Ser Arthur exuded class and dignity, not only living his life as a deadly warrior without peer, but raising the status of all associated with Knighthood. Remembered as good and valiant man, even by his enemies, I would definitely want him as my champion in a trial by combat.
2: Ser Barristan "The Bold" Selmy: Ser Barristan Selmy is a living legend. Riding in his first tourney at the age of twelve, earning his epitaph the bold, Ser Barristan is a seriously dangerous man. Making his name in the War of the Ninepenny Kings, Ser Barristan cut a bloody swath through the ranks of essosi and claiming the life of Maelys the Monstrous, The final Blackfyre contender, Ser Barristan certainly earned his spot on the Kingsguard. His legend didn't stop there, when his King (Aerys II) was captured during the Defiance of Duskendale, Ser Barristan infiltrated the Dun Fort, rescuing his king and avenging his sworn brother in the process. Serving well into his 60's, Ser Barristan was rudely dismissed from service in the Kingsguard, but found new life when joining the last (Apparently) Targaryen, Daenery's Stormborn. Still as dangerous as ever, Ser Barristan has certainly earned his place as one of the greatest swordsman in history.