Keep it simple. I really dislike:
The thumbnails that only show a close up of a small part of the picture, forcing you to click every picture to see it.
Slideshows that force you to view pictures in the order and speed presented.
Galleries that are too interactive, that scroll too fast or too slow when you are trying to check them out
Galleries that try to get too creative just get too annoying.
To answer your question a bit more on point, good quality pictures that give a good indication of you is what I look for. Some full body shots, with and without clothing. Some that feature your best asset, whatever that might be.
If it's obvious she is hiding a 'flaw', that turns me off. I am not looking for perfection, but I want to know what to expect. If there are only a couple of blurry pictures or a few close-ups, I don't take the plunge. This is a general statement, as I don't know at all what you look like, but I think you are better off finding clients who like you as you are, and not getting people disappointed at the door. That's backpage shit. I would assume most want more.
And put a picture in your ads on the boards. Sometimes I can't be bothered to click through to a website, the disclaimer, the flash intro, the gallery intro, just to see a picture of someone who was never my type to begin with.
Is it the lady's face, legs, butt, breasts....? Simple answer...yes. We all have different tastes. I like long legs, and pictures of long legs in stockings will get my attention every time. But a perfect ass or breasts will too. Have a gallery that hits all these things. Do a leg shot, a cleavage shot, an upskirt tease, a hair shot. If you keep the gallery simple, we'll see the one that piques our interest and you'll have us hooked.
And back to my original comments, if you hide that picture that we will like behind an animated thumbnail, slideshow, or close-up thumbnail that doesn't show the whole picture, we might miss it, and move on.