I know it's a little lame but I have to say my favorite anime outfit is Sailor Moon.
From her original Scout uniform, to her Super, to her Princess Serenity dress, I just think she's beautiful! I've dreamed of cosplaying her since I was a little girl! Of course it was just dress up then, but the dream lives on ^.^
All I need is my Mamo-chan to cosplay with me >.< @VinMcCarthy