I moved to the UK about just over a year ago from the US, and went through the same analysis. At the time I was AA Gold (solely due to good luck in travel scheduling).

Your #1 consideration should be how you will be able to earn, particularly on your long-haul flights. If your primary travel will be discount coach, then BA EC is probably not for you. I (and many of the Americans in my office) use AAdvantage, as then we get full credit when traveling to the US on personal business, and European travel on BA is mostly on business and thus earns 100% AAdvantage credit as well. Personal European travel is hopefully on BA (due to OneWorld status), but giving up the paltry 25% BA miles to save a few £ is a fair trade. This may not work as well for you, as to my knowledge none of the OneWorld partners from the UK to Asia (QF, CX, BA) offers full credit for discount coach--though if you earn enough miles on other flights you could instead redeem miles for your Asian flights.

Another consideration is elite qualifying partners partners, especially for long-hauls. UA/LH/BD (Star) and BA/AA (OneWorld) of course look particularly appealing here. VS has some good relationships as well, but elite benefits do not carry over to partners (and qualifying for elite based on partner flights is difficult).

Another significant consideration should probably be an airline that offers good schedules and routings to your frequent destinations. For example, you mentioned west coast USA. AA recently announced a 3rd daily LHR-LAX; I'm not sure about BA and VS (and UA?) schedules.

As a further note, if you are currently CX elite, note that Star Alliance is currently matching status. Ther are several threads explaining the mechanics and details, but if you can acquire a UK address in time (e.g. business/school address) you could get your CX status matched. For example, I just had my AA status matched to BD.