We fly ATA Chicago Midway to MCO three or four times a year. Chicago and Indianapolis are major ATA hubs (home office is in Indianapolis), so you can fly non-stop to a number of vacation destinations at reasonable fares (including LA, San Francisco, and Las Vegas). ATA is a good, no frills airline. They fly 757s along with smaller 737s. Many of their planes are quite new, and all appear to be in excellent condition. Express check-in kiosks at Midway and Indianapolis speed the trip through the airport at busier times. The only shortcoming we've found has been somewhat slow baggage handling (at both MCO and MDW), particularly compared to what we've experienced on Southwest. This is not a big enough problem to make me go back to flying United out of O'Hare. I would definitely suggest you give ATA a try.
Ralph