I liked Buffy's Yummy Sushi pjs. Also, Xanders various uniforms, not to mention Anya's bridesmaid gowns, what was the line... Oh, yah, "Radioactive".... But my favorite, Buffy's Doublemeat uniform!
But in al seriousness, I loved Anya's wedding dress and Buffy's prom dress, but for everyday... I think that Buffy looked, well, like Buffy in Becomming (1 & 2), Amends, Enemies and Grave.
I think that Willow looked adorable all through Season Three.
Also though, I think that what the actors makeup, hair and demeanor at the time affect the way I feel about the outfits.