The only non-stop from MEM to LAS is Allegiant. There have been occasions where their schedule was just right for me either outbound or returning. But, that seems to have been tweaked to either 6am flights out or ridiculously odd times back home. So, its either SWA connecting in either DAL, HOU or DEN. Delta is my preferred carrier since I earn a lot of points on my DL AMEX. But, connections are mostly through ATL and now they have added SLC as a connecting city which isn't bad.