While I love to attack United, it is fun, sorry. I don't see how leaving the alliance is going to help you, as it sounds like Thai Air will still come in handy if you are flying to Thailand.

Northwest is the only one I can think of, as NW and UA are really the only 2 US carriers that do Asia. NW works with Malaysia and Garuda, in case that helps.

Qantas(O/W) is near irrelevant, unless you are coming from Australia, with a couple of intra-Asia routes.

As for Cathay Pacific(Oneworld), it depends if you buy full fare coach or Business. They give fewer, and in some cases, no miles on discounted flights, something which is very typical in Asia. Why you are better off on a US airline, if you fly on the cheap...

Also, all that CX will do is get you, via Hong Kong each time, to Bangkok, with one flight onward to Singapore.

So, unless you see NW helping you, which is good in Business, fyi, I would stay with UA...

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Michael
AA PLT,1 MLN Miles+
HH GLD, SCI GLD, MM SIL
LE PRESIDENT ETERNEL DE CAMAIR-CAMEROUN AIRLINES