I know you know this but the highest priority pilot (setting aside FAA, etc.) is an AS pilot on company business (i.e. new hire on observation flight) and pilots agreeing to give up their deadheading seats in the back. Apparently this is the culture at Horizon and some have carried it to Alaska.

As far as commuting, you have priority on AS but not Horizon flights. Priority is year of hire within other commuters. JS is first-come based on who checked in as a JS, so make sure you check in as a JS even if you think you’ll get a seat in the back.