I try to avoid Southwest for a very good reason: No advance seat assignments.
My husband had to take his mother to Sacramento last year, and Southwest was the only non-stop option. We had to pay an extra $10 each way ($40 total) for early check-in, just so they had a decent chance of being able to sit together.
I called the airline and asked if there was any way they could guarantee an 84-year old woman could sit next to her son, and they said the early checkin was about the only thing we could do. They would not offer early boarding, as she is not in a wheelchair.
I look at the giant line outside T-1 at LAX (Southwest terminal) and shudder.