Tom911 presents it well.
As someone who travels SFO/NYC from time to time, I can tell you which airlines have the best rides, but that's all about "up front" and that doesn't apply to you, unless you have a reasonable chance of sitting there. And the only one where you will with mid-tier status is AS. Once MVPG, you'll also receive some upgrade products that you can use on lower (but not the lowest) fares at time of booking - this is in addition to the regular complimentary upgrade scheme. For the time being, and hopefully for quite some time to come, AS gives you full earning on all fares, has a pleasant (although not great in the F&B department) JFK lounge, uses a pleasant SFO terminal (probably one of the nicest in the USA) and should have a lounge open late this year, and generally has pleasant crews.