aktchi

Don't let the tail wag the dog. Common sense suggests you should credit your miles to the airline that you fly the most. That would maximize your benefits in many tangible and intangible ways. If you make Emerald or Sapphire, you can get some benefits on other alliance partners too. So BA, QR, JL, CX, whichever one you fly the most for long-haul flights.

I agree that BA's J product is sub-par. I won't recommend AA's program these days: their miles are hard to use, and you won't get lounge access on their domestic network. Nevertheless, if you fly AA domestic a lot, then the possibility of upgrade would be a positive. So there are pros and cons to balance.