Allegiant and Spirit aren't considered to be at the same level that the U.S. legacies are. The primary difference, ignoring past contract differences, is the ability to fly wide body international flying. It can be a very good deal in the U.S. Actually sitting reserve on w/b fleets is one of the most desired jobs in the U.S. The larger planes pay more and you work less on reserve. Non-commuters drool at that option.