[MENTION=190924]lixiaojuventus[/MENTION]
I was/still am a FlyingBlue Gold member, I did it for lounge access. However I'm switching over to Delta this year. With FlyingBlue, I earned on segments. But now that's not a feasible option anymore, as a US based flyer.
With Delta, you'll only need to worry about MQM's. In general, you'll earn these based on the exact distance you fly. There are exceptions, of course. If you fly in a higher class of service you'll earn a bonus. Or if you fly an airline that's not tier one, you'll earn fewer, with some Skyteam fare classes earning 0 MQM's. Check out
this page to see what you'll earn based on the marketing carrier of the flight you're flying. China Eastern has been a sweet spot for me this year.
Since Delta doesn't fly an international first class like AF does, you won't be missing anything with that, other than not being able to use your Skymiles to redeem flights in first. And as others have asked, how often do you do that anyway?
For earning Skymiles, it's about how much the actual ticket cost (not including taxes and fees), multiplied by various numbers depending on status level. Partner marketed flights earn based on distance. The above link will tell you how much and with which airline and in what fare class.
I'm assuming you have a foreign address which is how you don't need to meet the MQD's? I'm also assuming you're US based though? If yes, as a US based traveler, Skymiles is a better program for you.