After completing Cindered Shadows DLC, Yuri actually makes a pretty excellent M!Dancer. Combined with his Relic Accessory, he has quite a bit of durability/survivability.

I made Felix my dancer for my Blue Lions playthrough. He became unstoppable. (And looked fantastic in the outfit)
I'm playing Black Eagles now and trying to choose between Dorothea and Linhardt.

Deam I Sylvain became my dancer

I chose Marianne, as I'm playing a the blue lions and planning having an entire party of cavalry. Mostly consisting of holy knights, and maybe a dark knight and a bow knight or two of each if I can spare the slots when I get that high of a level.

I made Raphael my dancer ....

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can get levin sword limited via weapon shop. or you can refine a steel sword into a levin sword.

actually there are magic weapons too, Levin sword is a good choice here. its shock magic.

It says Dorothea is usually a healer/support, she actually is more suited to be your mage. But I will agree she is a good choice for a dancer since she can still use magic and is already proficient with swords.