I have to echo RiteSideUp's comments. We interviewed together and F9 is truly a class act. From the CEO to the clothing sales clerk; everyone seemed genuine and happy. Not only that, but they went out of their way to make you feel welcome and get to know you. Their QOL sounds pretty good too - one of the most flexible scheduling policies in the industry, even if you're junior.
I agree with those who mention commuting. I wouldn't have as much fun commuting to any job as living local, so that's something you have to ask yourself. I've heard JB is awesome too and yes, their growth plan is more agressive, etc. It's very tough with the dynamic nature of the industry to make a career choice based on anything other than pure QOL. That and a reasonable look at a company's financials. If a company can compete and thrive (which I believe in) based on customer service, attitude, and sound decision-making at the corporate level, then I believe companies like Frontier, JetBlue and AirTran will all do just fine. If not, I hope to never look back with regrets, because based on what I've seen of F9 I sincerely doubt I will have any.
Best of luck in your endeavors.
M3