1 Oberyn Martell
Oberyn Martell is a fictional character in the A Song of Ice and Fire series of fantasy novels by American author George R. R. Martin, and its television adaptation Game of Thrones. Oberyn could have beaten The Mountain! He tried so hard, but unfortunately he got overconfident at the end and that was his downfall.
2 Sandor The Hound Clegane
Sandor Clegane, nicknamed The Hound, is a fictional character in the A Song of Ice and Fire series of fantasy novels by American author George R. R. Martin, and its television adaptation Game of Thrones. This guy is just such an awesome fighter - unlike his brother, he's actually skilled as well as being really strong. It would be interesting, if not just awesome, to see him fight against the likes of Jaime Lannister in their primes, in my opinion.
Lets get Sandor over his brother!
3 Brienne of Tarth
Brienne of Tarth is a fictional character in George R. R. Martin's A Song of Ice and Fire series of fantasy novels. She is a prominent point of view character in the fourth novel, A Feast for Crows, and a main character in the television adaptation. In truth, in the show she has won the most fights out of anyone. However, few of those have been completely fair. She beat a (weakened)Kingslayer, an (injured)Hound, and of course, Loras Tyrell. Those are most of the great warriors in the series, and she has killed countless other knights and solider says well. While others may be better, we might not have yet seen the full range of her abilities. But she has a better argument for best fighter than most.
4 Gregor The Mountain Clegane
Ser Gregor Clegane, nicknamed The Mountain, is a fictional character in the A Song of Ice and Fire series of fantasy novels by American author George R. R. Martin, and its television adaptation Game of Thrones.
5 Jon Snow
Jon Snow is a fictional character in the A Song of Ice and Fire series of fantasy novels by American author George R. R. Martin, and its television adaptation Game of Thrones.
6 Jaime Lannister
Jaime Lannister is a fictional character created by American author George R. R. Martin. He is a prominent point of view character in Martin's award-winning A Song of Ice and Fire series, and also a main character in HBO's adaptation of the series, Game of Thrones.
7 Bronn
Bronn is a fictional character in the A Song of Ice and Fire series of fantasy novels by American author George R. R. Martin, and its television adaptation Game of Thrones.
8 Barristan Selmy
This man was well past his heyday, but he still managed to cleave through a horde of Sons of the Harpy. I'd honestly love to see him unleash his true skill in a one-to-one duel with someone.
9 Khal Drogo
Khal Drogo is a fictional character in the A Song of Ice and Fire series of fantasy novels by American author George R. R. Marton.
10 Arthur Dayne
Arthur Dayne 1-on-1 kills any of the choices above with the possible exception of Selmy, and a 2 handed Jamie having an outside chance.
The Contenders
11 Arya Stark
Arya Stark is a fictional character created by American author George R. R. Martin. She is a prominent point of view character in Martin's award-winning A Song of Ice and Fire series, and also a main character in HBO's adaptation of the series, Game of Thrones.
12 Jaqen H'ghar
13 Eddard Stark
Eddard "Ned" Stark is a fictional character in the first book of George R. R. Martin's A Song of Ice and Fire series of fantasy novels and the first season of its television adaptation.
14 Daario Naharis
Daario Naharis is a fictional character in the A Song of Ice and Fire series of fantasy novels by American author George R. R. Martin, and its television adaptation Game of Thrones. Daario hasn't lost a single fight, and has some pretty impressive feats. He started out in the fighting pits, and eventually earned his freedom, became one of the three most feared mercenaries in Essos, then killed the other two. He was one of the elite team that took Yunkai, and killed dozens of Harpies in the fighting pit. We haven't seen him pitted against most of the others on this list, but he certainly has a fair chance against any.
15 Jorah Mormont
16 Ramsay Bolton
Ramsay Bolton, also known as Ramsay Snow, is a fictional character in the A Song of Ice and Fire series of fantasy novels by American author George R. R. Martin, and its television adaptation Game of Thrones.