I've done domestic F on UA, AA, NW and also the PS F on UA(although the overall sample would only be a dozen or so).

I have been generally impressed by AA to be honest. PS would win out on the seats and IFL lounge access, but the crew still had that "go hide in the galley" mentality that I haven't seen on AA (but perhaps I'm just lucky?)

UA & NW left me wholly indifferent. I remember a 2hr UA flight up the west coast & the food offering was peanuts in F!

Also, PS isn't on the SEA-BOS route so it's a moot point anyway.

Watch out for flight times - it's "funny" what they don't consider to be a flight worthy of serving a meal on...