4 definitely pop to mind.
1. Kas'im - he mastered every single form (for every primary art of the saber; regular, dual and doublebladed), then spent decades refining his skills and perfecting every single move and sequence, and he was also a master of switching between his forms. He was also completely dedicated to his saber skills, and only his saber skills, practising as much as he possibly could (and I really mean that, he didn't sleep for instance, and practised instead).
2. Ulic Quel-Droma - after having been cut off from the force, and out of practise for 20 years, he was able to stalemate a very powerful jedi master/war champion who was being fueled by the darkside at the time. This is extremely impressive, given the extent a jedi uses the force while dueling (reflexes, precognition, augmenting senses, physical attributes etc.), and judging by Traya's descriptions in KotOR 2, a jedi completely depends on the force, and without it, he is even lesser than a non force user, because of the reliance.
3. Mace Windu - after having mastered multiple forms, he was able to create Vaapad, the most deadly of all forms, and the one that is hardest to master. Only three ever mastered the form, and Windu was the only one who didn't turn to the darkside. He was a saber genius.
4. Kyle Katarn - he was able to defeat 7 powerful dark jedi with no training whatsoever, that's damn impressive. Just refer to Mokoto's arguments.
Then it contradicts your topic title, genius. The best pure swordsmen implies this is a contest of who's the best swordsman, disregarding the force. It should be called "The Best Technical Swordsmen." Buts its all irrelevant, I already apologized for not reading the topic thoroughly (I tend to skim your posts)