I would go with AA. I find their CS easier to reach, even if you have to settle for a callback. North American based call agents are easier to work with
in case of schedule changes in my experience. Went through fifteen changes over a fourteen month period. I found AA agents quite helpful in my situation, willing to open I space on any of their flights and willing to use OW codeshares also, unlike BA agents who could not offer more than what their computer allowed.