Alaska and DAL you just show up at the gate. Just did a listing on SWA for the first time and it worked great.
The only negative about DAL and Alaska is a significant portion of their SEATAC staff are somewhat "knowledge challenged". That is a politically correct term for it. I had one day where an agent didn't know how to do a JS on both Alaska, and another day on DAL, and watched one day as two FA's tried to do an ID90 on Alaska, unsuccessfully.
One time I missed the flight, one time I had to buy an ID90 last minute, and the two FA's didn't get on.
All the last 6 months. Poor training for newbies maybe. Both always treat me great when I get on.