Definitely dresses, although skirts and sleep wear are a close second and third. When it comes to clothes, I’m as girly as they come. Anything plain in bras, panties, etc. is definitely out.
FYI, part of the reason that I waited so long to transition is that my clothing preferences are very atypical of women. I have several female friends whom I’ve never seen in a dress or a skirt. I’ve been going to the same nail salon for four years; in that time, there have been four times whrn either a customer or a tech (besides me, of course :)) wore a dress or a skirt.