Why does everybody assume southwest's fares are always lower?
Price out PHL-SEA from June 18 return 22 and get the following:
WN - $507.20
US - $405.20
And with US, there is only 1 cnx vs. 1 cnx. + 2 stops on WN.
Sure, WN has lower fares showing on those days, but they're not bookable.