1. Hires you
2. Stays in business until you're able to either (a) retire or (b) get hired by a "better" airline.
Plus, it's in a constant state of "flux" in determining the "best" airline. Usually, the airline that's best today, is usually the worst tomorrow -- once upon a time, UAL was the best because of lots of growth, the very best pilot bases, fast upgrades to captain and being able to hold international 777/747 FO within 6 to 18 months after being hired.
Sadly, they're teetering on extinction today.