Which airline offers the better deal depends on numerous factors, such as arrival and departure cities, flight time and when the ticket is purchased. As of July 2015, Allegiant Air typically flies based on customer demand out of smaller airports, according to the Allegiant Air website. Spirit Airlines has more than 250 daily flights and more than 50 destinations.
Get a good airline deal by booking at least 6 weeks in advance, choosing the earliest flight of the day and flying on a Wednesday, recommends U.S. News & World Report. Travelers wishing to compare flights between Spirit Airlines and Allegiant Air can do so by checking prices on each airline's website.