We use to love flying ATA, but they no longer fly out of Indy ...
Then we flew Northwest for a few years and they were great ...
We are flying Airtran down to MCO this year for our December trip (earlier non-stop than NW so we are going to give them a try.) However, we are still flying Northwest back to Indy (we can check in our luggage at our Disney resort the day of departure and print our boarding passes as well ... that means more time at the parks, less hassle going to and at the airport.) Airtran was talking about becoming a participating airline but I have not heard that it is official yet ... you can't check in your luggage when flying southwest and for us that is a big disadvantage.