Legacy airlines are quickly losing ground to these low-cost carriers.
France, Île-de-France, Paris . Le Marais, Place (square) des Vosges in autumn (fall)
Credit: Getty Images

Budget airlines are constantly touting their flash sales and no-frills fares (like $70 transatlantic flights with WOW Air, or Frontier's celebratory $20 domestic tickets). But are they really the more affordable option when there isn't a flight deal involved?

In September, The Telegraph looked at the cheapest direct flights from London to a number of popular holiday spots (Madrid, Berlin, Rome) and found that low-cost airlines are elbowing out the competition on most — but not all — major routes.

To see if the same thing was happening closer to home, Travel + Leisure asked the flight search engine Skyscanner to identify the airlines offering, on average, the cheapest tickets to in-demand domestic and international destinations.

For the 10 most popular cities for outbound flights in 2017, Skyscanner determined the average ticket price — and the airline offering the most competitive fares on that route.

On all 10 routes, budget airlines edged out legacy carriers.

Top 10 Most Popular Destinations

New York City was the single most popular destination this year for flights originating in the U.S.— and Allegiant Air will typically offer the best price. Their round-trip tickets to New York City cost $165.33, on average, versus the industry average of $296.26.

That’s more than $130 in savings.

To the second-most popular destination for U.S.-based travelers, London, WOW Air had the most affordable tickets. On average, travelers will spend $565 round-trip with the Iceland-based low-cost carrier, while tickets with other airlines cost $755.30.

WOW Air also had the best price on flights to Paris ($560 versus $680.50), making it the most affordable airline for Europe-bound travelers.

Spirit Airlines had the best ticket prices on six of the 10 routes, including cheap flights to Miami, Los Angeles, and Denver. And for San Francisco-bound fliers, Frontier Airlines offered a modest $43 discount, on average.

Of course, travelers who save on face-value tickets with budget airlines need to be extremely cautious about ancillary fees. Unlike full-service airlines, the cheapest carriers often charge for advanced seat assignments, checked (and sometimes carry-on) luggage, and in-flight food and drinks.