Originally Posted by
pilo
DL has devalued its miles with the 3-tier structure. That being said, it is far easier to earn miles on DL (they constantly do 30-50% bonuses, etc).
In the end, the smart thing to do is to keep them in SPG account until you actually need to *use* them, and then transfer to whoever has availability.
...knowing that SPG transfers to airlines can take a week to two weeks to complete (last AA one I did from SPG took 7 days)