It depends upon the flight, sometimes Avios are the best deal and sometimes AA miles are best. Avios are fixed prices but increase with distance whereas AA miles are dynamic, and (usually) not related to distance. Select a longer distance flight and the Avios required will increase significantly, whereas the same flight on AA miles will likely change both up and down randomly over time. With Avios you have to pay for each flight in a connecting itinerary, whereas all segments are included with AA miles.

BA makes all award seats open to booking with AA miles, whereas AA can be quite stingy making award seats available to Avios. BA charges huge fees on transatlantic awards whether booked by AA miles or Avios but fewer miles whichever program is used. AA charges much lower fees but (usually) much higher mileage amounts when booking with AA miles although there are occasionally bargains to be had. AA allows last minute cancellations at no charge, whereas Avios have no refund whatsoever of miles or cash when cancelling with less than 24 hours notice.

So, it depends upon your travel patterns and primarily what distance your flights are, whether there are non stops or not, if you have a need for last minute cancellations, if you value miles over cash on transatlantic flights, if you are looking to predominately fly on AA or BA and a host of other factors. Availability of AA flights using BA miles can be a real problem. If you can do it, it’s best to have miles in both programs because sometimes AA works out best and sometimes Avios.