As mentioned, this largely depends on what fares you are on and what you are planning to do with the miles you earn. JAL and CX are distance-based with a fare-class component, yes. AA is revenue-based for AA flights, but distance-based for partner flights. Carefully research your options, especially if you (have to) fly economy. For example, only the highest, very expensive economy fare classes on Cathay earn any miles in AAdvantage - so you'd be better off crediting discounted Y tickets to Marco Polo where they earn at least something and contribute to attaining status.
Banking miles for (much) later use is only possible with AA because JAL and CX have fixed expiration policies - miles are gone after three years no matter what (exceptions apply for top tier status holders).

BOS to HKG/Asia and return is between 15k and 20k miles per trip, so you would make at least medium-tier sapphire status on all programs. If you fly Premium Economy or business class, Emerald is attainable. I would not rule out AA in this case, as the 4 systemwide upgrades you receive upon qualifying at the 100k level are pretty valuable, allowing you to upgrade two return flights on AA no matter the fare class of your tickets. AA F may not be an especially aspirational product, but I can attest that it's a very comfortable and spacious way to spend a 13-hour flight . JAL only allows upgrading with miles on very expensive tickets in comparison, so not suited for the average traveler buying discounted fares.
Independent of FFP earning options - if you (have to) fly Economy, JAL is the only airline with a decent product on both aircraft types it uses on its TPAC flights. They are the only airline with 8-abreast seating (2-4-2) and corresponding seat width on all 787s, and they retained 9-abreast seating (3-3-3) on the 777s where all other airlines squeeze passengers 10-abreast in super-narrow seats nowadays. This makes a world of difference to me, and I`d not fly anyone else for this reason alone if I had a choice.