Before a recent Virgin America flight from San Francisco to Seattle, I decided to credit the miles earned on the flight to my Alaska Airlines loyalty account instead of my Virgin America account.
Because I’d already booked the ticket with my Virgin loyalty number, I had to call up Virgin America to make the change (they don’t allow you to edit that online, though I could have entered my Alaska number initially when booking).
Why credit the flight to Alaska?
With Alaska, you earn miles based on how far you fly.
Even on Virgin America flights, if you credit the flight to your Alaska account you’ll earn the amount of miles that you fly.
With Virgin, you earn miles based on how much money you spend, as it is with most airlines now.