I think a major question is what are your motivations? Domestic lounge access?

Qualification is rarely easier, earnings aren't really better unless you're specifically targeting Avios earnings (it's still not better, just different currency), and award charts generally quite as good outside of 'sweet spots'. I definitely use BA/QR as supplementary programs, but keep AA as my primary for a multitude of reasons mostly noted above.

Personally I don't care about domestic upgrades as I seldom fly domestic so it's not a big deal and often just buy F when I do. I also don't care about domestic lounge access since my purely domestic itineraries are even rarer. But AA's award chart in many regions is pretty competitive and awards that don't touch North America are readily available on partners for good redemption value. AA's EXP line is excellent, UA's 1K too, not sure which is better in my experience.

I honestly can't imagine jumping ship for anything except BAEC Gold or QR Platinum, but the use case would need to be more specific vs. flying a lot of OW partners as I tend to do.

I can make a similar argument for AS but we don't know the new award chart yet, it could tank the program's appeal or they could take a similar chart to AA. But with the removal of required segments, their top tier is extremely easy to achieve this year.