I really enjoy Southwest airlines service. It is not overly convenient for me as they have a limited presence in airports under an hour from me, but I have been known to drive 90-100 miles to use Southwest.
A little-known fact about Southwest is that if you have a high seating number within the C list, you are at risk of not getting a seat at all. If the flight is overbooked, then all of the seats will be full when you get to the plane and the gate agent won’t let you on to the plane.
I never fly Southwest without paying the slightly higher cost of Early Bird seating. This will typically get you place in line in the mid-to-high A list, or in a really popular flight, a low B number.