It is only up to $40 to cancel and re-deposit. It's the lesser of $40 and the taxes and fees paid, which, yes, for domestic travel within the United States is just the $2.50 per segment AY (September 11th Security Fee) capped at $5.00 per one-way trip.

So if you're booking domestic travel, you should always make two separate one-way reservations in case you plan to change one of them. That way you just cancel the entire one-way and re-book it, paying just $2.50 instead of the $40 change fee.

Also, it seems like people neglected the OPs actual question: 10K BA is a no-brainer. American miles are valued generally around 1.8cpm (since they don't charge fuel surcharges except on BA and IB) and their First and Business awards are much more competitively priced than BA. For instance SFO-HKG-SFO in F on CX is 210,000 Avios + Fuel Surcharge, but 135,000 American + Airport Taxes. Avios are valued closer to 1.2cpm, but are super easy to earn via transfer from both Amex (almost always with a bonus of over 20%) and Ultimate Rewards.

So 17,500AA are worth ~$315 and 10,000 Avios are worth ~$120.

tl;dr: Go BA. Less miles, each of which is worth less. Taxes are the same.