To bump an old therad, again...
Dooku takes all.
Sabers wise, his domination of Kenobi is SoD and TCW, him statlemating/edging out Kenobi in RotS and him besting Ventress and Pre-TCW Grievous outclasses all Arcann has done.
Force only is closer, but I still see the Count taking it. His ragdolling of Kenobi and Vos is at least as good, imho even better, than Arcann ragdolling an weakened Outlander, Arcanns feat against a heavily weakened Valkorion doesn't proof that he is above Tyranus, imho. Also, Tyranus challenged Yoda with his lightning.
Last, but not least, Dooku's toying with Cruisers is impressive af.