I travel all.the.time for work, and after the first year of trying different airlines, I determined SW is the best option for regular fliers. Been trying to fly them exclusively for about four years now.
-Two bags on the flight - no charge
-Two checked bags - no charge
-No black-out dates for points
-Guaranteed first-choice seating (A List) after, like, 8 flights
-Points accumulate quickly and can be used affordably
... plus, the greatest airline perk there is - the Companion Pass: I haven't bought a second ticket for my wife in a couple years now... if I buy a ticket (often with points), I get her ticket free.