Totally depends on the girl. Blue jeans and a white t-shirt always looks good on a girl IMO.
I used to see a provider who always met me at the door wearing some sort of dress or skirt. I'd drop the envelope on the table and we'd start the session immediately, sometimes without even saying hello. On the table, on the couch, on the floor by the door....just hike the dress up and off we'd go. It was a huge turn-on knowing that we'd be making it within seconds of her opening the door for me. I was a regular and we had a trust factor going which made it possible. I was always done in 20 minutes too, which probably made her happy.