Can you buy Economy Comfort/C+ tickets for your travel? I ask because Delta's probably the most humane experience for non-elites/low level elites among the Legacy 3 carriers. And you can credit Delta flights to the air France-KLM Flying Blue FF program on a distance flown X fare class multiplier so economy comfort flights booked as such get 125% of distance, which will often get you more miles in a program where redemption rates are often slightly less than going with Delta metal.

Flying Blue has a lot of dance partners in the credit card realm- the right card from Citi, Chase or AmEx will let you transfer miles into there. Flying Blue also has its own US credit card now, which makes it somewhat easier (but not exactly easy) to get XPs for elite FB status (The XP earnings for US domestic routes on Delta are insultingly low)

For non-C+ tickets, FB is less of a sweet spot though, and the cheap fare bucket multiplier is only 25% x miles flown

https://www.flyingblue.us/en/partner...s/presentation

Do note that for American, they try to push you off to BA and their heavy YQ/fuel surcharge on award tickets for transatlantic award flights and their low level domestic award availability is not great these days either.