The tally favors Delta over United.When people in the U.S. think about flying, Delta Air Lines (DAL 0.74%) and United Airlines (UAL -1.25%) might be the first companies that come to mind. They both have large market capitalizations and many travelers have flown with one or the other, but they employ very different strategies. Because of this difference, investors can tell which airline is truly first-class.Different tracksUnited CEO Scott Kirby is betting on initiatives such as adding planes and making upgr ...