Showing what I think the outcome would be in a duel between these two legendary Sith. Like Anakin was able to kill Dooku, I think Darth Maul would do the same. Maul has high level skills with a lightsaber combined with an aggressive fighting style, like Anakin. Dooku could use Force lightning, but it would not help against Maul, who knows dark side abilities, and would just block it with his lightsaber.