Four inches.

It is the length of a cell phone. It is two chapsticks end-to-end. It is a little bit more than the width of the widest part of a tie and a little bit less than the width of a Polaroid picture. It is not only the only reason to fly American Airlines, but also a reason so compelling so as to make American the airline of choice for many frequent fliers. The four inches that make American the best of the major US airlines can be found in the extra space between your knees and the seat of the guy leaning all the way back in front of you in coach.

While you may not miss that four inches on a quick jaunt between New York and Washington, on a flight of any length, it is the difference between getting there and getting there with your knees and legs intact.

In many ways, American is about the worst airline one could imagine. It is constantly teetering on the verge of bankruptcy, having never maintained profitability over a significant period of time. It is operated by gate agents who cringe at sharing the most basic flight information, flight attendants who are (on a good day) surly and worried about keeping their jobs, and pilots whose avarice is almost soley responsible for both the fiscal crises plaguing the industry and the creepingly higher fares. Moreover, the business and first class services are but shadows of what one can expect for the same price -- especially across the Atlantic -- on airlines like BA or Virgin.

But for most travelers, those four inches make all the difference.

Oh...did I mention that almost all seats have power ports so that you could work on that spreadsheet or watch the entire first season of the West Wing on DVD.