awww.. that's not fair. Grouping Southwest with Spirit!?!? They are both discount airlines, but I let the similarities end there. The closest relative to Southwest would have to be Jet Blue. Southwest has the "no assigned seating" policy. You get an A, B, or C boarding assignment. Print your boarding pass at home 24hrs before takeoff and you are almost assured of the A group. Spirit is assigned seating and a relatively new company in the sky. Spirit's planes are more comfortable. The seating on the Airbus jets is more comfortable than the Boeing 737's of Southwest. They both have comfortable deluxe leather seating but Spirit offers the "Big Front Seat" for passengers who want to have a little bit more wiggle room. They are very nice!! You can't book them for a roundtrip oddly enough. On Spirit you will pay $1 for every soda and $5 per beer, glass of wine, or liquor drink. On Southwest, sodas are free and liquor, glasses of wine, and beer is only $4. (just went up from $3) Spirit is much more limited in flight schedule and airports serviced. (Although, at least Spirit services Atlanta) Spirit has some great intro rates that they are currently offering which makes them very attractive. I guess the only other drawback to Spirit is that you can only travel with a full size chainsaw if it is in your checked baggage.
P.S. It is kind of ironic that Southwest's corporate inflight magazine is called "Spirit Magazine."