Just to be clear, we are talking about villains in general? (i.e. they don’t have to be the antagonist)

In that case:

Saga of Tanya the Evil has got Tanya, who is not only extremely badass as a villainess, but also serves as the series’ protagonist.

Otherwise, my pick goes to Quinella from Sword Art Online: Alicization. She is evil but with cause (whether the cause is good is another debate).

Also,

mild SAO:Alice spoiler

she went down with style.

Honourable mention goes to Askeladd from Vinland Saga. I begrudgingly respect him despite his evil acts.

Also,

mild Vinland Saga spoiler

he went down swinging.