Southwest is my airline of choice. Not that it's necessarily my favorite, but it wins by default because it flies out of the airport closest to my house (Midway) and because it goes to most/all of the domestic destinations that I'll probably ever go to.
My most recent flight with Southwest was awesome on the way TO Vegas and puzzling on the way back home. On the way out, we had an all male crew. I've never felt safer and they all had such awesome personalities that I daydreamed about becoming a flight attendant so we could go city-to-city and hang out on the weekends. They were a great representation of Southwest and of good customer service. This was probably my favorite flight that I've taken so far.
My experience back (Vegas to Chicago) was just...odd. When the flight attendant was doing the safety schpeel, she was laughing the entire time. Not just giggling - hysterically laughing. What a way to make me scared as hell that my flight attendant is off her rocker if there IS a legitimate safety concern. I thought it was super disrespectful especially since all of the passengers on the flight had no idea what was going on. At least bring us in on the inside joke so we're not just staring at you like you're crazy.
Overall, Southwest is a great airline. You still get free snacks, bags are free, airline personnel are usually pleasant (if not a little erratic) and you can usually find a good deal on their website-- oh and I'm almost up to a free flight in the RapidRewards program so make sure you sign up even if you don't travel that much.