Importance order for me:

1. Legroom
2. Footroom
3. Limitation or absence of recline from in front of me
4. Shoulder room
5. Cushioning
6. Total width of butt space

(Never really thought of the height of the seat or armrest as a big variable between airlines.)

I can control 4 and 6 by selecting an aisle seat. An aisle-side armrest that lifts can help with 1, 2, and 6.

As for Southwest, they're either going to narrow the aisle of the total shoulder room has to stay the same, right? I mean, they didn't reinvent math down there in Dallas, did they? They aren't changing the height of the seats or floor of the aircraft to get a wider fuselage at butt-level. When I'm in a window seat, my shoulders are already wedged tight against the wall, so even if they somehow get my butt an inch closer to the sidewall, by shoulders are still just as wedged. The only place to "steal" space is a narrower aisle. Maybe WN can pull it off since they don't use drink carts, but isn't there some sort of FAA standard on aisle width? Seems like airlines would all already be operating at some sort of legal limit there.