These are the 2 best credit cards for racking up airline miles

If you're going to spend money, you might as well get some free airline perks while you're at it.

We consulted NerdWallet, a personal finance website, about which credit cards were the best for getting free air miles and other rewards. As it turns out, it's not easy to get a straightforward answer because it largely depends on which kind of flyer you are.

That is, if you're someone who flies a particular airline regularly, it's best to just get whatever credit card that airline offers and call it a day, Sean McQuay, NerdWallet's credit card expert, told Business Insider.

American Airlines, Delta, and United Airlines all offer frequent flying cards with good rewards options, McQuay said. Those three airlines' frequent flyer cards also come with a low annual fee of $95.

But if you're interested in a card that provides flexibility so you can convert points into miles on any airline, McQuay said the best option is the Chase Sapphire Preferred Card.

"Compared to other options, like Capital One Ventures, Citi Prestige, [and] Barclaycard Arrival Plus... Chase has the best transfer partners [where] you can use those points with different airlines," McQuay said.

The Chase Sapphire Preferred awards two points for every $1 spent on travel and dining and one point for every $1 spent on anything else. Users have the option of transferring their points to several different frequent flier programs - including United, Southwest, and British Airways- or they can book a flight via Chase Ultimate Rewards and get 25% more for their points.

Additionally, if you spend $4,000 within the first three months of opening an account, you're eligible for 50,000 bonus points. You can also receive more bonus points for referring another person.

Business Insider's Tanza Loudenback was able to book over $600 of air travel for free using the Chase Sapphire Preferred over a six-month time frame. Getting two points for every dollar spent on travel and dining is a particularly good deal, she points out, as you're getting bonus points for spending money on things like metro cards, Ubers, taxis, and Seamless.

The card's APR ranges between 16% and 23% and a reasonable annual fee of $95, which is waived the first year you open the account.

But the Capital One Ventures does have one slight advantage over the Chase Sapphire, which is that you can book a ticket before you earned your sign-up bonus and then retroactively put those points toward your travel costs via a credit on your statement, McQuay said.

"That's a niche and specific use case, but if you have travel coming up in next few months and know you want to earn a credit card sign-up bonus in time, that's a great way to go," McQuay explained.

The card offers a sign-up bonus of 40,000 miles if you spend $3,000 on purchases within the first three months of opening an account. What's more, you get two miles per dollar spent on all purchases. The annual fee of $59 is waived for your first year after opening an account and the card's APR ranges between 13% and 23%.

If you frequently take international flights, McQuay said it's also worth considering the British Airways Visa Signature Card because it has a good sign-up bonus with a relatively low spending requirement. Those with the card get 50,000 Avios (or points) for spending $3,000 within the first three months of opening an account.

The card also has several transfer partners, like Aer Lingus, Alaska Airlines, and Meridiana. You can also use it on American Airlines flights.

"With that, I emphasize it only works if you're traveling with that airline, otherwise I would look at more flexible options," McQuay said.