American vs. Delta vs. United - we compared the 3 most popular airline credit cards and named a winner

The United Explorer Card from Chase is a solid option for United flyers.

The United Explorer card offers 40,000 United miles when you spend $2,000 in the first three months. While the card has occasionally offered higher targeted bonuses, those don't always waive the $95 annual fee for the first year — this current public offer does.

Like the other airlines' sub-$100 cards, the United card offers a free checked bag for the cardholder. Up to two traveling companions booking at the same time can also get a free checked bag each. This is especially useful since United recently raised the price of a checked bag to $30.

Unlike the other airlines' cards, though, you'll have to actually buy the tickets with the United card in order to get the free checked bags — simply having the card open and tied to your account isn't enough.

For those who don't have luggage to check, the card offers priority boarding for everyone on your reservation — you'll get this benefit even if you pay for the tickets with another card. By boarding earlier, you can make sure to snag overhead space for your carry-on.

One excellent perk with the United card is that you'll get two complimentary passes to United Club lounges each year. If you get to the airport early or end up dealing with a delay, you can head to the lounge and enjoy free snacks, drinks, Wi-Fi, and more comfortable seating than what you'd find in the terminal.

When you spend $25,000 in a calendar year, you'll also get a PQD waiver — PQDs, or "Premier Qualifying Dollars," count toward earning elite status with the airline. When that requirement is waived, you'll earn status just based on how much you've flown, rather than a combination of how much you've flown and how much you've spent that year.

The card earns 2x miles per dollar spent on all United purchases, and following the card's rebranding in June, it also earns 2x miles on all dining and hotel spending. It will continue earning 1x mile on everything else. There are no foreign transaction fees.

Other features include a fee credit to cover the cost of enrolling in Global Entry/TSA PreCheck, and a 25% discount on all in-flight United purchases.

One unique — but unpublished — perk of the card is that having it helps you access additional United award space. That means that you'll have an easier time finding the flights you want when it's time to actually use your miles.

Click here to learn more about the United Explorer card from Insider Picks' partner: The Points Guy.

Until April 3, the Gold Delta Amex is offering 60,000 bonus Delta SkyMiles when you spend $2,000 on purchases within the first three months. You'll also get a $50 statement credit if you make any Delta purchase with the card within the first three months. In terms of points, this is the highest-ever public offer on the Gold card.

In addition to the welcome offer, the card comes with a handful of incredibly useful — and valuable — perks.

If you have the card open, you get a free checked bag on Delta flights, as does each other person on your reservation. Delta normally charges $30 for the first checked bag on each flight — so $60 for a round-trip — meaning that for a family of four, the free checked bag benefit could save $240.

The card also offers priority boarding to everyone on the cardholder's reservation. If you aren't checking a bag, that can come in useful — by boarding a little earlier, you'll get better access to the overhead compartments and won't have to worry about space running out.

For those who travel periodically, but not often enough to justify investing in a lounge membership (or getting access to Delta Sky Club lounges through the Amex Platinum Card), the Gold Delta SkyMiles card also offers discounted day passes to Delta's lounges: $29 per person. That can be a useful backup to have in case you ever find yourself with a long layover or a delay.

Other benefits include a 20% discount on in-flight purchases (in the form of a statement credit), such as food or drinks, and no foreign transaction fees.

The card earns 2x Delta SkyMiles on every dollar spent with Delta, and one SkyMile per dollar spent on everything else. The card has an annual fee of $95, which is waived the first year.

While the Gold Delta card is a great option, you may also want to consider the Platinum version (the Platinum Delta SkyMiles® Credit Card from American Express). Although it has a higher annual fee —$195, not waived the first year — it offers a companion pass each year on your cardmember anniversary. Plus, it currently has a welcome offer of 70,000 SkyMiles when you spend $3,000 in the first three months — also until September 19. You can learn more about the companion pass benefit and the Platinum SkyMiles card here.

Click here to learn more about the Gold Delta SkyMiles card from Insider Picks' partner: The Points Guy.

Each card has strengths and weaknesses. Let's look at each:

American Airlines: the Citi/AAdvantage Platinum Select

Pros:

• 2x points on dining and gas — not just on airline purchases
• Offers a solid sign-up bonus
• Free first checked bag for you and up to four traveling companions, regardless of whether or not you use the card to buy your tickets
• Priority boarding
• $100 discount on an American Airlines flight if you spend $20,000 in a year
• Discount on in-flight purchases

Cons:

• No lounge passes or discounts
• No spending bonus that counts towards elite status

United Airlines: the Explorer Card from Chase

Pros:

• 2x miles on dining and hotels, as well as on United purchases
• Two complimentary United Club lounge passes each year
• Priority boarding for you and your travel companions
• Discount on in-flight purchases, Global Entry/TSA PreCheck credit
• Access to additional saver-level award seats

Cons:

• To get the first checked bag free, you'll have to use the card to buy your tickets
• The free checked bag is only extended to up to two traveling companions — that's not helpful if you're traveling with a family of four

Delta: the Gold Delta SkyMiles card from American Express

Pros:

• Free first checked bag for you and any traveling companions, regardless of whether or not you use the card to buy your tickets
• Priority boarding
• Discounted day passes for Delta Sky Club lounges
• Discounts on in-flight purchases
• All-time highest public welcome offer (until September 19)

Cons:

• No bonus earning categories (besides Delta purchases)
• No extras (like a discount on flights, extra points, or help toward elite status) if you spend a lot on the card in a year

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 the new benefits, including 2x points at several new 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.

In a similar vein, the current limited-time welcome offer on the Gold Delta card makes now an ideal time to open it.

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 Citi/AAdvantage Platinum Select card from Insider Picks' partner: The Points Guy. Click here to learn more about the United Explorer card from Insider Picks' partner: The Points Guy. Click here to learn more about the Gold Delta SkyMiles card from Insider Picks' partner: The Points Guy.

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.