So, which is best?

The best card is the one for whichever airline you find the most useful. Although there are some differences between them, each of these cards comes with a version of free checked bags and priority boarding, which are the most valuable reasons to have the cards. Plus, they help you earn more miles — and quickly.

However, if you're ambivalent about your choice of airline, the Citi/AAdvantage card for American Airlines is probably the most appealing card right now.

Between 2x miles on several categories and a solid sign-up bonus, this card represents a great value. However, keep in mind that it's always possible that the sign-up bonus increases at some point in the future, although there's no guarantee.

However, starting on January 30, 2020, the Gold Delta Amex will give the Citi AAdvantage card a run for its money thanks to the introduction of new bonus categories and perks.

As benefits continue to be added and removed — and, crucially, as sign-up bonuses and welcome offers fluctuate — this evaluation could always change. One way or another, an airline card is a must-have and represents significant value for anyone who flies even just a few times a year.

Click here to learn more about the United Explorer card. Click here to learn more about the Gold Delta SkyMiles card.

This content is not provided by the card issuers. Any opinions, analyses, reviews or recommendations expressed here are those of the authors' alone, and have not been reviewed, approved or otherwise endorsed by any issuer.

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