Every airline shopping portal is (almost) the same store underneath

Open the American AAdvantage eShopping portal, then open the United MileagePlus Shopping portal, then Delta SkyMiles Shopping. Click around. Feel that déjà vu? You're not imagining it. Most of the U.S. airline shopping portals run on the same underlying platform — a white-label service (Cartera Commerce, if you want the name) that a dozen airlines quietly share.

Same merchant catalog. Same tracking pipeline. Same "click through, then shop" mechanics. The only real difference is which airline's miles get printed on top of the transaction.

Why this matters more than it sounds

If the plumbing is shared, then two things follow that save you real time:

• The list of stores barely differs between airlines. If Nike is on one airline portal, it's almost certainly on the others.
• The earn rates move in loose lockstep, but not perfectly. The platform is shared; the promotions each airline funds are not. So one airline will occasionally out-earn the rest on a given store during a bonus.

That second point is the entire reason a comparison tool exists. Here's one merchant across the airline portals right now:

When those miles-per-dollar numbers are equal, the mechanics behind them are identical — so the tiebreaker is simply which miles do you actually want?

So which airline portal should you use?

Since the store list and tracking are basically the same, pick on the miles, not the portal:

• Value the miles you'll actually redeem. United miles, AA miles, and SkyMiles are not worth the same to everyone. Choose the currency you have a real plan for.
• Watch for the funded bonus. When one airline runs a "spend $X, get bonus miles" promotion or bumps a store to an elevated rate, that's the week to use that airline's portal. Our rate changes feed surfaces those jumps.
• Mind the welcome bonus. New to an airline's portal? Several offer a first-purchase bonus — United's, for instance, hands new members bonus miles for a small qualifying spend. One-time, but free.

The honest takeaway

The airline portals want you to think of them as distinct destinations. Under the hood, they're mostly one destination wearing different logos. Use that: shop the store you were going to buy from anyway, compare the miles across the airline portals on its merchant page, and route through whichever airline's miles you'll actually burn.