I won't even go into the sheer horror that happened when ATA switched over to online check in. I lost count of the times they screwed up our "assigned" seats. Even though we were Elite members, they often were NOT helpful.
With Southwest, if you print out an A boarding pass early and get to the airport early enough to be one of the first in the A line, you probably have a better chance of getting what you want than some of the so-called "assignments."
Barb