I was in the same boat at the OP. Also, like the immediately preceeding poster, I was dissatisfied with UA, particularly the poor state of my hometown LAX RCC.

It came down to switching to either Thai or Singapore, and I decided to go with Singapore, where I now accrue most of my miles. I still fly UA in the US and don't necessarily obtain an upgrade, but I don't care. I'm far more interested in using miles to upgrade when flying over the oceans, which the *A program should let me use my Singapore miles for.