If you don't care about MQD, MQM earn (which will be mileage-based in both cases) should generally be identical in same class of service with one significant exception (DL Basic Economy fares no longer earn MQM, miles, etc. while AF Economy Light fares still do). Redeemable mileage earn can be considerably more on AF fares for cheaper premium cabin fares due to being mileage based vs. spend based, but generally don't differ that much for cheap economy class fares.