As much clothing as is possible for her to wear while still allowing penis in vagina. Frumi's point about the christmas present unrwapping is spot on, a girl in clothes is a present waiting to be unwrapped and I'd like to do that while fucking her.
I'd leave shoes and stocking, hats and other accessories on the entire time though. But sometimes it's fun to fuck a girl bottomless, with just her shirt on, or if she just takes her panties off and keeps her skirt on, but hikes it up. Full nude is obviously good, but I think it's something to be savored and kept special. If every girl gets full nude instantly every time, it becomes a bit bland. A choice between getting with a girl that's fully naked, and a girl that's only wearing a scarf, I'd go with scarf girl provided both girls are identical twins with no major body differences. Same if she's wearing high heels, a garterbelt or some other kinky item. It's also good from a color perspective.