For me, it all depends on where I'm going, how long the flight is, etc. I love JB..it's my airline of choice. But, if I'm going with just a carryon bag, then any airline, with good times and prices, will get it done for me. If I can use JB, I will...even if it's a bit more costly. But, I won't spend more than an addtl $25 to fly them.
When we fly out to Ca next month, we wanted an airline that had good times, shorter flights (hopefully non-stop), and the ability to get a credit if we are forced to cancel. JB filled those needs. Yes, SW would have given us a full credit (unlike JB that charges $100 for a change), but SW had not so great flight times, no non-stop, and the fares were quite a bit higher.
So, with JB, I get the inflight tv, one free checked bag pp, a bit addtl legroom, decent cancellation cost, and the flights I wanted.
It all boils down to ....
flight times
cost
free checked bag
tv's
legroom
I will pay a bit extra for those things.