1. Expedia
As a naive travel newbie, I would book flights through Expedia because it seemed consistently cheap, had a rewards system, and was easy to use.
After a few negative experiences with customer service (which can happen with any third-party flight-search site) — including an incident with a missed connection that had me running between help desks at the airport — I stopped purchasing tickets through Expedia.
I still use it as a search engine, however, since it offers plentiful filters and scores each flight out of 10 based on amenities and aircraft quality.
2. KAYAK
Priceline's KAYAK is reliable when it comes to finding deals. In an initial search, the calendar indicates which dates are cheapest with a green dot. It can predict price trends and indicate the best time to buy.
My favorite function, however, is KAYAK Explore. Perfect for the beginning stages of planning, Explore lets users plug in a home airport and rough idea of travel dates, then it displays a map of prices and destinations you probably haven't even thought of.
3. Google Flights
Google Flights looks similar to KAYAK but is often faster and shows the cheapest price for each day during the initial search, making it easier to select the cheapest departure date. Its calendar is perfect for a flexible and frugal traveler like me.
As with other websites, it allows users to track prices via email and explore price trends through a graph. Unlike others, it will even indicate the amount of legroom, the availability of power outlets, WiFi, and in-flight video.
4. Momondo
While more colorful than Google Flights, Momondo doesn't offer as much detail about the flight itself as its counterparts, which, for me, is much more important than website aesthetics.
On the other hand, Momondo categorizes search results into three tabs, labeled "cheapest," "quickest," and "best," under which I can easily find the best bang for my buck.
5. Skyscanner
Skyscanner is a godsend for booking international travel and is the best website for cheap flights, in my opinion. I personally use a variety of resources, but if I had to choose just one all-inclusive website, this would be it.
Like KAYAK, Skyscanner will help you choose the right destination for your budget by simply selecting "everywhere" in the "to" box. It lets users search loose dates and will even suggest the cheapest month to fly. It categorizes flights by "best," "cheapest," and "fastest," and — without fail — always offers the cheapest price.
For instance, in a search of round-trip flights from New York to London, all four other websites showed their cheapest flights for $520, while Skyscanner showed one for $512. For multi-city trips, Skyscanner is easy to use, too, allowing up to six destinations in one search. For a cheap traveler like me, Skyscanner is key.