If you need a airline flight to somewhere warm, travel agents say to let them book you. 

The indsutry has discovered significant price differences, by as much as a factor of two, between identical flilghts listed by on American Airlines and US Airways websites:  same flight, same plane.

JoAnne Verboom at  "Travel by Gagnon"   tells WOOD Radio it's due to the different technology platforms that the two airlines use. 

Mergers have created the cross-platform problem and she says until the two start using one "common technology",  the software that the travel agents use will be your best bet at finding  the lowest fares.