Hi Dave,
It all depends, but without any additional information, I would say SkyMiles.
I will still ask the questions, to see if it would change the answer:
- Are you flying C or Y? If Y, 90% SM (unless you are on a very cheap fare class which would not earn you miles).
- What is your fare class? Unless it's full fare or business, SkyMiles (again, the lowest AF fares don't earn SM, but will only earn 25% miles on FB)
- I'm assuming you are based in North America, so that would favor SM.
- Miles expiration:
- FB: it's after 20 months, and you can only extend by crediting a Skyteam flight
- SM: 24 months, and many more options to extend validity.
So basically, unless you are flying C (on the most expensive fare class, and even then) and you plan to fly with Skyteam at least every 18 months, go with SkyMiles.
Cheers,
GenevaFlyer