relentless1
Dark Overlord of KMC
Yoda is good but he couldn't get the job done against Dooku OR Sidious
Mace is also good but in the end he was bested, he's been stated to be on Dookus level and even if you believe he beats Sidous truly (he didn't) then you have to factor in his amp via Vaapad, which he wouldn't really have in any other situation.
Dooku is good but old, Anakin bested him simply due to age difference.
Anakin had potential but he allowed himself to be clouded by anger, making him sloppy.
Obi Wan is the best fighter, the only one he had a clear disadvantage to was Dooku and by the time of ROTS he could have arguably beaten Dooku but got caught by a Force push, for the sake of the plot IMO.
Even when fighting Maul, he pushed him to the limit, slicing his saber in half, Maul had to resort to Force push as well to get the upper hand again.
If anything you could say Obis weakness in saber fights is Force push, nothing to do with the actual sword fight itself, he picked Grievous apart rather easily which was 4 sabers against 1.
Judging by record alone you gotta give the nod to Obi Wan here.
2 Sith Lords and Grievous, the Jedi killer.