I hate above all else the feeling like you are sheep or cattle rushing on the plane to get your seat. I'm a fan of assigned seats. It doesn't matter if I'm first or last on the plane, I'm going to get my seat. This is especially annoying when I am travelling with my whole family. Trying to get seats all together is nearly impossible on SW.
Plus, their planes tend to break down more than most other airlines. That's because they don't buy new planes. They buy old, refurbished ones and as a result they have a higher than normal amount of delayed flights due to mechanical problems.
The solution to the checked bag fee, get a Delta amex, or AA or United if that's who you fly. Then I get a free checked bag every time I fly.