The number one thing I like about flying Southwest Airlines, is FLEXIBILITY. There are no change fees, so you can book your flights and have maximum flexibility if you change your plans.
In the past when I bought airline tickets, I would wonder "AM I GETTING THE BEST PRICE?". With Southwest Airlines, it is so easy to re-book your flights if the price drops after you buy. It took me only 5 minutes on the phone with Southwest to get my savings when a flight went on "sale". You receive a credit (that is linked to your confirmation code) that is very easy to use on future travel. Just make sure you keep track of the credit, and don't forget to use it (it expires one year after purchase date). Then, when you book a future flight online, it is just another form of payment...you enter the confirmation code and name, and it brings up the credit, and takes it off...super easy!
Southwest also flies direct (nonstop) to many of the smaller locations. This can save so much time! Usually, a direct flight option will cost less on Southwest. Unless the dates are really soon, and the flight options have been pretty well sold.
I also recommend their credit card, because they have incentives, giving new cardholders lots of points to use for free travel. I will say their fares correlate pretty closely to the points needed, so if you waited until the last minute to book a flight that has gone way up in price, you will also need a lot of points.
Seating
This is pretty different on Southwest. You do not get a seat assignment. What you DO get, is a place in line. When you arrive at your gate, you will have a letter and number on your boarding pass. Group A gets to line up first, and everyone in this group will literally stand up and get in order (it is kind of amazing how well this works, and how quickly people get organized in the line).I recommend you either pay an extra $15 for "Early Bird" check-in, so you will automatically get a queue number...usually a pretty good one. Or, if you are able to go online to check-in at 24 hours prior to your flight, they give out numbers, first-come-first-serve "style" which will print on your boarding pass. If you forget to do this close to 24 hours, you will probably get a lower queue number, like C40. A1 being the best. They assign A1-A60, B1-B60, and C1-.... Usually.
And no bag fees!