I personally prefer to follow CPA and ACO rules, since I think this game has the potential to be much more than just a backyard game.
TWO NOTABLE DIFFERENCES:
1) One notable difference between ACA and ACO/CPA rules are that for one, in ACO/CPA you have to stand directly across from your partner, whereas ACA you can rotate tossing in the same tossing box. ACO/CPA doesn't allow you to rotate in the same box tossing bags.
2) Another notable difference is that in ACA the contestant who scored in the preceding inning shall pitch first in the next inning. If neither pitcher scores, the contestant who pitched second (last) in the preceding inning shall pitch first in the next inning. Whereas in the ACO/CPA, the player/team who scored in the preceding frame shall pitch first in the next frame. If neither player/team scores, the contestant who pitched first in the preceding frame shall retain first pitch in the next frame.