Well Ive flown Jet Blue and Southwest.
Jet Blue is good now that they have the direct flight, however its only one direct flight a day so depending on what time you want to be in Orlando this can make or break your choice. I prefer them over Southwest because I actually get to pick my seat at time of booking. However thier prices can be tricky. It seems the farther you book out the cheaper the price can be.
Southwest was nice. They dont have tv's in their seats like Jet blue does however I belive they have more than one flight that is direct to Orlando every day. They give out snacks like jet blue does. Last year DS was 6 months old when we flew them and he loved thier plane crackers.. which are basically ritz crackers shaped like planes. Southwest made us sign a waiver that if anything happened to our gate checked stroller that they were not to blame, which Jet blue never had us do. It did get one tiny stress mark possibly from the cold on the snack tray but all in all it came out fine.
We are flying Jet blue on our next trip simply the time it arrives in Orlando and the fact we have a existing credit with them helps