In my opinion, I would take whichever one you did first of the regular (Bio or Chem)
I don't know how your school system works, and I'm assuming since you're a sophmore (Just taking a guess), I'd assume you took Bio first, like regular Bio. So I'd do Bio AP, since it's less fresh in your memory, and then I'd take chem.
My plan right now for my science classes are like this:
Freshman: Biology
Sophmore: Bio AP and Chem
Junior: Chem AP and either Physics or Psychology AP
Senior: Physics AP
TL;DR
If you took Bio first and Chemistry second, then take Bio AP first and then Chem AP
And vice versa, if you took Chem first and Bio second, then take Chem AP and Bio AP.
BUT, if you took neither of those classes (Regular Bio or Chem), then take Bio AP first.