Well, with One World you have CX and QF that fly pretty much anywhere you would want to go in Asia. BA flies pretty much anywhere you want to go in Europe or Africa. So taken all together, One World is in my opinion just as strong as Star Alliance.

Now what your upgrade chances are as a top-level elite at AA on these airlines is really only something that can be answered by someone who is one and has went through it.

But in my humble opinion, AA is better than UA, QF is better than NZ and BA is better than LH. Thus, on this basis, I view One World as a better alliance than Star. But this is just my opinion.