More Americans are choosing to travel internationally these days. In fact, according to CheapOair’s recent travel trends report, international air travel has increased by nearly 170 percent since 2013—with a 30 percent increase since last year alone.

Budget airlines tempt you with cheap fares, but they charge extra for everything from seat assignments to carry-on bags. Is it worth it? Which low-cost carrier is the best? And what about their frequent flyer programs? Let’s take a closer look at Allegiant, Frontier and Spirit.

You’ve heard about them before. Mileage runs–the holy grail of scoring tons of miles by using cheap fares to fly a long distance. Since airlines have largely adjusted the way they award miles (based upon price of the ticket versus distance flown), mileage runs have lost much of their appeal.