Why not the person who paid the highest fare? Nothing is worse than paying twice or thrice what others have paid for a last minute ticket, only to lose out on an upgrade because someone with an O fare bought it 3 months ago. Or how about going on customer LTV? If you make AA more money, you should go higher on the list. What about aggregate annual spend? If you're a big spender, they'll want you happy up front, right? There are a myriad of ways they could order upgrades--they had to pick one and go with it. I think I benefit from the status quo as often as I am dinged by it, so I just roll with it. If you frequently buy cheap fares, you may not like what other legacies are doing much better.