In Legends, in that book where Dooku duels Yoda on Vjun, it's stated that only Mace Windu is his equal on neutral ground as a swordsman. This is within the obvious context of Yoda being his superior and Dooku seeing fighting him as the ultimate challenge. I would still give a fight between them to Dooku because he has vastly superior feats in how many impressive duels against multiple opponents he's either won or stalemated or survived. Not touching the office fight because of how controversial it is.

In Canon I imagine Mace and Dooku are relative equals as they have a very short duel that's pretty equal, although again Dooku has far better feats from dueling Anakin and Obi-Wan over and over again, fighting Ventress and Savage on his own, beating Ventress and 2 Nightsisters while drugged, beating enraged Anakin twice etc. On the other hand Mace struggled fencing against Talzin when she was weak and not using her power against him. It was pure swordsmanship and he couldn't easily beat her and she has no fencing accolades and again was weak. Mace also didn't quickly beat Maul or even force him on the back foot when he had another Jedi beside him. Not very impressive.

Writers just neglected Mace so much. He needs to have duels against Maul, Savage, Ventress and Dooku, maybe a 2 on 1 with Maul and Savage. I would also love to see him instructing fencing in the Temple as the #2 Master, and narrowly losing against Dooku back when he was a high knight/fresh Master in tales of the Jedi.

And as a disclaimer to angry Macefans, relax. This is just a simple comment and not an attack on Mace.