Originally Posted by uastarflyer
You have it reverse - CX is AAdvantage, while SQ is Mileage Plus.
The answer to your question (if starting from scratch) is clearly Mileage Plus, since both SQ and UA both run non-stops SFO-TPE, no issues on mileage accrual, weird routings, etc.
And MP and Star Alliance are just simply better (more choices) when it involves Asia. If you want a high quality Asian carrier, SQ matches CX, and then otherwise UA runs many more flights into Asia than AA. Flying on UA and crediting those flights to Mileage Plus will have your account increase in a hurry. Either way you're covered.
What you have to balance is your "sunk investment" to date in AA.
Edited to add - you could ask to be comped to Mileage Plus Gold based on your Platinum with AA, and use these 4 trips to hit 1K...to even out your starting point.
I agree with all of the above. All things being equal I'd suggest UA and Star Alliance. Hope I'm not complicating matters too much by laying out other considerations to take into account.
My primary consideration if I were you would be which choice gets to 1K (United) or Executive Platinum (on AA). There is a big difference between those levels and the ones below them, not least electronic coupons that get you free international upgrades once you reach those highest tiers. I know more about UA than AA, but if the miles you stand to accrue this year fall short of 100,000 AA might be a better bet because, if I understand it's system correctly you also can reach EP by virtue of reaching 100,000 points and you get extra points (something like 1.25 or 1.5 per mile flown) for flying business class. (Someone who knows that system better might be able to correct or clarify what I am saying here.)
Which alliance you want to accrue miles with also might hinge on how: 1) how you want to use those miles (e.g., I'm mainly UA and Star Alliance but have recently taken a couple of trips on Cathay Pacific to cash in miles on American for a vacation in the Caribbean, a part of the world AA covers better than UA) or 2) where you mainly will be flying to and from for business in the future. If mainly flying from SF and/or to Asia into 2005 and beyond, UA and the Star Alliance are the way to go. Try to get UA to comp you up to Premier Executive based on your AA platinum status by calling the Mileagel Plus service desk at 800-325-0046. I've seen some posts indicating that if the first agent you reach isn't helpful you could try again with another agent, but in any event I believe UA's general policy is to comp this status if you have equivalent status on another airline, perhaps especially AA.
Having said that, if long-term mileage accrual and use aren't that important to you, the SF/Asia travel point doesn't apply, you place a higher premium on accruing miles in the short term, and/or you don't care about flying non-stop between SF and Taipei, you'll bank more miles by flying SF-Hong Kong-Taipei on Cathay. Your August and September trips in effect will net you 325% on the SF-HK-SF legs (note that you must register for this special) as opposed to 225% if you get Premier Executive on UA.
I'd add that I prefer SQ to Cathay because in my experience, while both are better than UA and AA, SQ is a more flexible airline to work with (quick to offer free hotel rooms if your ticketing means you must pass though Singapore for several hours or overnight, for example), but I don't want to distract this thread with that debate.
If I haven't talked this choice to death, you might try posting your question on the UA and AA forums of Flyer Talk. I think more people might read your question at those locations.
Hope this all isn't too confusing!