^I don't really have much more info than that lol.
It really depends on how tight you want them and your comfort level. Don't expect to be able to move around easily if you size down. They'll stretch, but it's not a fun process.
I don't think the sizing varies by the wash, I initially found the veggie wash ones in a 27 and bought them since that was all I could find (it was a size up from my TTS).