If you like the fit of other 2Xist underwear, you'll feel a bit odd in these.
It's made for people with big bellies, and tiny legs. I run, and bike, and box, so my legs are thick, and my stomach tight.
These are not made for me.
I have a 29" waist, but wear 32"x34" regular jeans, to fit my thighs comfortably. I bought a medium. This should give you a good idea about the shape and fit of these.
If the elastic around the legs was the same as the the waist, it might be better, but the legs elastic is really tight, and has very little stretch. The waist, however, is very soft and loose elastic, with lots of stretch without feeling tight.
hope this helps.