Even if you know for sure that it's the one with the larger comb that is laying, I wouldn't be concerned. The one with the smaller comb is likely just maturing more slowly. Chickens are like people; they mature at different rates. :o)
Pics would definitely help here. How old are your Buff Orpingtons? If they are at least 14 weeks old, the one with the smaller red comb is likely a pullet getting close to laying and the one with the larger red comb and wattles is likely a cockerel. However, without pics I can't be certain.