I always like Southwest. Two free bags, no charge for seats, done in numerical order. The staff is usually exceptionally friendly as well. They need more direct flights coast to coast, and the one downside is that they have NO reciprocal relationships with any other airline, so if the plane doesn't make it or the last SW flight is cancelled, you are STUCK.
They need to negotiate harder on the flight reciprocity with other airlines. Other than that, my top choice.