We generally fly Southwest, since they are the only airline flying direct from our city (St. Louis) to Orlando. That makes the choice easy, especially for a short (2 hour) flight. We are not crazy about the boarding procedure but do love that they don't charge for bags, have friendly service and make it easy to cancel or change a flight without losing all the money you have already spent. Southwest has also sent us great rental car offers close to our flight date, particularly for Orlando and Las Vegas.
We were pretty loyal to American a few years ago, but St. Louis is no longer a hub and there aren't many direct flights. Plus, American took away our ability to meaningfully use upgrades and began charging for checked bags.