I have had good, bad and weird experiences w/ Athleta. I bought several items over a year ago, and hated the way everything fit, and had to send it all back. Which I had to pay for. So, not too excited about that part of it, since you can't return it to a Gap co. store. Recently I bought several things w/a 30% discount and free shipping, which is why I finally bought again. I bought 3 different bottoms, and wound up needing 3 different sizes. I would say I usually wear a size . I needed a size 0, 2, and a 4. I had call and do exchanges, it was kind of a drag, but their CS was friendly. Their sizing is definitely not consistent.
I bought a bathing suit the first time around, and the fit was so terrible. That was just my experience, but a bathing suit is hard to buy online.
I have not paid full/regular price for anything I've bought there, and I probably never will. I did get a Gap credit card over a year ago so I could take advantage of more of the free shipping offers that are given to CC holders. I have asked them (via customer comments) to offer free return shipping, since we can't see the clothing until we order it, but nothing has come of it yet. I have heard that they are interested in opening Athleta stores, but I'm not holding my breath on that happening where I live any time soon. Have you tried Lucy activewear? I really like their bottoms. Good luck!