It all depends where your hub is. If you're in America and you fly mostly coach and earn upgrades or use VIP's it's tough to let go of AA which gives ExecPlat's 8 upgrades a year (without any restriction on booking class) which I've always been able to use or give to my wife with minimum hassle. That's a very valuable resource. Africa coverage is light, but that's only an issue if one is traveling there often. Cathay is top notch in Asia and they treat Emerald's very well. Access to the F lounges despite your booking class is worth a lot too.

My real issue is LHR and the transfer between terminals by bus which is an enormous and inefficient pain. However, once you make your way through the morass of British inefficiency the lounges at T5 really are great, and I don't have experience in the F lounges in *A, but it feels like the really good ones (LH HON) are restricted to F tickets only, which means they're not really an advantage of being in an alliance and rather available only to dollars spent - which trumps any loyalty rewards for any alliance.

The one big issue in OW if you're American is that you are stuck with AA for all TATL flights because of the non compete with BA. This is a real bummer and *A really beats everyone here since you can choose between CO, UA and LH to get overseas and compare fares, timetables etc.

I have been considering a move to *A because of the LHR issue - which will get worse and worse with the recent whackjob failed attempt on the DL flight Xmas Day - but loathe to figure out if I bought the correct class to use a SWU , have less of them, and get the same or inferior lounge product when connecting after a long LAX to wherever in Europe jaunt across the Pond.