Some airlines are looking extremely attractive, but some are looking like broken business models.Although airlines are traditionally thought of as capital-intensive and money-losing businesses, Delta (DAL 1.52%) has done a fantastic job diversifying its revenue stream and delivering profits. On the other hand, one airline that used to be widely regarded as the best investment in the industry doesn't look like a great buy at all. Watch the short video below for all the details.*Stock prices used were the mor ...