Oh man. I love so many costumes, I'd have to break it down into tons of sub-categories (costume I most want to wear? costume I would hire someone to make if I won the lottery? costume I thought was a great fit for the character? costume I thought was iconic if not necessarily noteworthy?). They're usually from fantasy/sci-fi or period pieces, which...does not narrow it down.

I have gotten to see museum exhibits of Star Wars and Black Panther costumes, so they probably get honorable mention because I've seen them in person.