AA's large number of flights and ability to work with other carriers has been great from all that I have seen.

Recently flew WN and was reminded why I stick with AA. After 'heavy fog cancellation in MDW' the next time they could get me home was two days later than booked and that was flying through MSY or something. They absolutely refused to put me on another carrier even though everyone else (AA,UA,Delta) was still flying to ORD, albeit a little delayed.

I called the EXP and asked for same day (honestly same-hour) saaver award availability and found the seat I needed! I asked agent to book who even suggest I call the carrier I was on and get them to endorse the ticket over at which point I said, 'I wish I wasn't on Southwest'. Agent booked the ticket and I flew home just an hour later than originally planned. Major props for AA's ability to do this.