Fujitora and Mihawk haven't fought yet, so until they do Mihawk is the greatest swordsman. Fujitora's df ability would probably win the fight for him, but that wouldn't necessarily make him the greatest swordsman then.
I think Mihawk is crazy strong personally. We got to see him so early on and he's still around. Honestly I think the main reason he can be yonko level is because he doesn't have a crew, that we've seen. His status and lack of crew may have led him to be warlord even though he probably deserved better.
If there was any "clan" to fix the Noah it would be Tom the Fishman's clan. Iceburg and Water 7 plus his cousin/brother and his workers from fishman Island. And if Franky can go he'll be there too. This is just my best guess though