For me, it all depends on the situation and mood.If we're in a sexy mood outdoors and doing something casual, I'd like her to be in a dress/skirt and shirt with no underwear.
If it's indoors and we're just hanging out, a sexy one piece lingerie. If it's a sexy time, then stockings, with crotchless thong, a sexy bra and some accessories which I like. And during sessions, ponytail with a little make up, no bra, sexy thong and the collar.
Again, it all depends on our mood, the situation and the level of power exchange at the moment.