Delta's basic economy restrictions are the most generous of the big three. With a basic economy fare:
You can't reserve a seat before check-in, and are not guaranteed seats near traveling companions.
There are no same-day ticket changes — including if you miss your flight or standby for an earlier flight.
You're ineligible for complimentary upgrades (if you have elite status) or paid upgrades.
You'll be in the last boarding group, meaning all the overhead storage space may be gone by the time you board.
In the grand scheme of things, that's not too bad. But not being able to sit near traveling companions — or getting stuck in a middle seat — can be inconvenient, as can running out of overhead room and having to check your bag.
While there's no way to get around the inability to pick your seat — besides paying to upgrade to a regular economy fare — holding any of the regular Delta co-branded credit cards gets you priority boarding on any flight, regardless of whether you use the card or not.
The best version is the Gold Delta SkyMiles Credit Card from American Express. With priority boarding, you'll virtually always be able to find overhead compartment space. The card also offers a free checked bag for each traveler on your reservation, so you can just drop your bag off when you get to the airport if that's what you prefer.
Until April 3, the card offers 60,000 SkyMiles when you spend $2,000 in the first three months, plus a $50 statement credit when you make a Delta purchase in the first three months. The card's $95 annual fee is waived for the first year.
When you buy one of American Airlines' basic economy fares:
You can't choose your seat in advance.
No changes to your ticket are allowed.
You're ineligible for any kind of upgrade.
You'll board in the last group.
Like with Delta, you might have trouble finding overhead bin space since you'll board last.
Also as with Delta, the American Airlines credit cards offer priority boarding to cardholders, regardless of whether you use the card or not. Because of that, American specifically exempts cardholders (and elite status holders) from the carry-on restriction.
The best option is the Citi/AAdvantage Platinum Select World Elite Mastercard. In addition to priority boarding, the card offers a free checked bag to you and up to four companions, and a 25% discount on in-flight purchases. It also earns 2x points at restaurants and gas stations, as well as on American Airlines purchases.
For a limited time, the card is offering an increased sign-up bonus of 50,000 miles when you spend $2,500 in the first three months. The card has a $99 annual fee, waived the first year.
Generally, United's basic economy is considered to be the worst of the three, partly because the costs of buying up to regular economy can be exorbitant. Restrictions include:
No advance seat assignment unless you pay extra (you'll get your seat at check-in or at the gate).
No flight changes or refunds.
MileagePlus elite credits won't be earned.
You'll be in the last boarding group.
You're not allowed to bring a full-size carry-on — only a small "personal item."
You can only check-in online or through the United app if you're checking a bag. Otherwise, you'll have to check-in at the airport.
If you have a United credit card, you'll get priority boarding, and, in effect, be able to bring a regular carry-on bag on board — that's because the rule is enforced by not allowing anyone in the last boarding group, all of whom are on basic economy fares, to bring a carry-on with them.
You'll also get a free checked bag, although you must use the card to purchase your ticket in order to get that benefit.
If you try to bring your larger bag and you don't have priority boarding from the credit card (or elite status), you'll have to pay the checked bag fee plus an additional $25 "gate handling" charge.
The best card option for United flyers is the United Explorer Credit Card from Chase. The card offers 40,000 miles when you spend $2,000 in the first three months. While the card has occasionally offered higher targeted offers, those typically don't waive the $95 annual fee for the first year — this current public offer does.
In addition to the free checked bag, priority boarding, and ability to bring a carry-on when flying basic economy, the card also offers two complimentary passes to United Club lounges each year.