Is Dooku > Vader?
(This applies to Legends)
The evidence from this comes from their respective performances against Obi Wan. Multiple sources, perhaps most in detail the Death Star novel, confirm that Obi Wan had weakened from RotS to ANH, and that Vader was understandably taking the fight seriously. Said sources also describe the battle as either an impasse or a modest tilt in Vader's favor, but hardly as a curbstomp.
Meanwhile, Dooku basically f*cks up Obi Wan at his strongest with minimal effort, first pushing him down and then ragdolling him while kicking Anakin away.
Why didn't Vader just do that if he really were so strong in the Force? You could say that he wanted to make it personal or something, but this doesn't fit with his musings in the Death Star novel, which make it clear that he was leaving absolutely nothing up to chance. The other explanation is that Obi Wan declined as a duelist but grew considerably stronger in the Force - this is possible, but never really mentioned or hinted at in any of the source material. And none of that would refute the evidence that Dooku is the superior duelist.
After all, we know that the original intention was for Vader to be a shell of his former self, a view that changed after TFU unleashed came out. So Vader's edge over Dooku in Legends comes primarily from his spectacular feats in one franchise. Are those feats even better than Dooku's own cruiser ragdolling?