Ok, I voted Other, simply because I have a difficult time pinpointing an exact size. I have everything from S to XL in my closet and the same is true for my intimates... I'm almost 5'9, and a size 10 through the waist, but my thighs are a little bit curvier than most size 10 women, as I'm athletic and have more muscle in my legs, both thighs and calves. I'm also naturally a size 40D. A good amount of the time, I wind up either going up a size in order to customize my clothes to fit over the twins yet not look like a tent over my stomach, or can't wear size 10 jeans or pants unless they have some level of stretch to them so they will fit over my thighs yet still have a good fit through the waist rather than pucker.
With lingerie, I'm usually a medium as lingerie usually has more give to it then regular clothes. I don't do flannel or PJs, I'm a satin, silk and lace nightgown type of girl ALL the way... but if I want something really sexy and skintight, I can never find anything that fits me right as I'm a contradiction in my measurements. I'm a ten through the waist, probably closer to a 12 through the thighs, then a 40D in the chest.
I think the most important thing for me is lingerie based on not only S, M, L, or XL, but cup size as well as those are usually easier for me to determine whether or not they will fit properly.