It has to be Aayla Secura. I mean how could you not get distracted in the fight? Nobody could resist taking a peak at those blue boobs. And that's all she would need to cut you down, one quick glance and you're dead. They should have had her fight the Palpatine instead.
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During the Clone Wars, I'd say Anakin, Windu, Yoda, and Sidious were among the strongest duelists. I'd put Obi-Wan up there too but he has a knack for getting knocked out during a fight. Still, his calmer composure allowed him to defeat Anakin. I'm a huge fan of Ahsoka's fighting style though.