For girls, Good Society runs TTS to maybe 1/2 size big. if you are on the small size of your size, size down, otherwise, stay with your usual size. I got a 26 and it doesn't stretch out a ton (have worn 10x now), so I am pretty happy that I stayed with my regular size and didn't size down. i have the straight leg.
I have the Good Society skinny legs and after 2 months wear have stretched a lot!!!! I went down in size by one just for reference.
As for APC...I am a lady but owned the Hipster selvage and I sized down 3, I also have the bootcuts full selvage and only sized down 2. So it will depend on your cut as well.