What makes the biggest difference in comfort on any flight, regardless of airline, is having an empty seat next to you. And if your flight is full, that’s something which is largely within your control when flying on Southwest Airlines. If you fly Delta you hope they didn’t assign the seat next to you. If you fly Southwest, seats aren’t pre-assigned, so you hope no one decides to sit next to you.
There’s a whole subculture of people who have their own strategies for making sure sitting beside them is… undesirable.