I''m 5''2" and 115lbs. I like this in a size small. I usually wear an XS in TYR suits but this one is good in small because the back coverage isn''t full. I have maybe a slightly larger than normal butt, nothing special. I believe the small is going to stay put during most surf sessions and playing in the surf.  Very flattering. Would like it even more if it had an internal drawstring, but it doesn''t and I''m happy.