We compared Google Flights and Kayak to find out which one is better for booking travel, and there's an obvious winner

Let's start with standout features both services have in common. Both Kayak and Google Flights let you track flight prices over time.

If you're not ready to book yet, both Kayak and Google Flights let you track a specific flight over weeks or months.

Both services will also let you know if they think it's a good time to buy, based on historical data.

Both Kayak and Google Flights show you what they think are the best flights.

Google says it shows you flights that "give you the best trade-off between price and convenience, based on factors such as duration, number of stops, and airport changes during layovers."

Kayak says its results are based on duration, price, number of stops, and carrier type.

There are several key differences between the two services, though. For one, Google Flights is faster than Kayak.

Google loads almost instantly, but Kayak takes a few seconds:

Google will show you a price graph, so you can see how flights compare over the next few months.

I find this feature very useful, since I'm often shopping for flights when I'm considering visiting friends and there's no specific date I want to go. It's helpful to see if flights will get cheaper sometime in the future.

Google will also show you all the other prices of flights that depart and return around the same time you're looking to fly. If you're trying to decide between leaving on Friday or Saturday, this will help you decide.

Both the price graph and flight insight features are built into Google right on the main page of the site, so it's easy to check them out, then get back to browsing.

Google Flights can predict delays.

Google introduced a feature in January that will let you know if you can expect flight delays before you even book your flight.

Google says it uses historic flight status data and machine learning to predict delays, even if airlines haven't released that information. Google says it only flags those delays when it's 80% confident.

Google Flights will tell you about extra perks, like how much legroom you can expect.

As a relatively short person, this isn't a key feature for me. But for those who require lots of legroom — or anyone flying on a red eye or long flight — knowing the legroom situation ahead of time is a nice perk.

But Kayak has a leg up on Google in a few ways. It offers a few more filters, so you can be more selective with your flight.

For the most part, Google Flights and Kayak have all the same options for filtering your results.

But Kayak tosses in a few extras, like filtering out regional jets or only booking flights that have Wi-Fi.

Kayak shows you the entire trip at once, while Google Flights only shows you one leg of the trip at a time, starting with your departing flight.

For me, one of the frustrating things about using Google Flights is that it typically only shows you one leg of the flight at a time. I like to get the whole picture at once, and Kayak shows you the entire trip right up front.

Kayak lets you search for other things besides flights.

This may not be useful for everyone, but it's a feature I find myself using all the time. My hometown is in the same state where I currently live, and I'm usually trying to decide between flying and driving when booking a trip home. On Kayak, I can switch back and forth between car rentals and flights without switching to another site.

Kayak also lets you search for hotels, cruises, and deals.

There's one major difference between Kayak and Google Flights, and it's what makes Kayak the clear winner: Kayak finds cheaper flights.

In 20 tests of flights all around the world and at different times of year, Kayak found cheaper flights more often — sometimes by only $2, other times by greater amounts.

Only three times in those tests did Google Flights find the cheaper flight.

This wasn't a scientific test, and in many situations, Kayak and Google Flights surfaced identical results. But there were so many instances where Kayak beat Google Flights on price that I have to assume that it's the superior service.

Now, not everyone is always looking for the cheapest flight possible. I'm usually trying to find a balance between cheap and convenient, but I typically err on the side of what will cost less. Knowing that I'm seeing the very cheapest option available on Kayak is comforting, even if I end up picking something slightly more expensive.

Google Flights offer plenty of cool perks, and it has a much cleaner, easier-to-use interface. I much prefer the experience of searching for flights on Google Flights over Kayak.

But it's hard to ignore that Kayak finds cheaper options. So while Google Flights is an excellent service on its own — and I'm probably going to start using it more often, at least for comparison's sake — Kayak remains the winner.