The people I know who’ve picked UA over SWA lately have been younger (25-35 years left in their career) and able to afford a riskier career with greater upside in terms of diversity of aircraft and flying. They’ve also mostly been east coast and UA bases were the same distance or closer than. SWA bases with a greater spread between upgrades at UA (<5 yrears) and SWA (>= 10 years) on the east coast.

i do know some who went to SWA and stayed there. #1 priority seemed to be base, #2 QOL. (17 days off right away vs 12-13 at UA).

In your case I’d say go to whoever gives you the first class date, then go to Delta for the SEA base. If you want WB flying go to UA after SWA while you wait for DAL. That way if DAL never calls you still have quick upgrades on the 73 and the ability to do widebody flying.