Update: Some offers mentioned below are no longer available. View the current offers here.“Reader Questions” are answered twice a week by TPG Senior Points & Miles Contributor Ethan Steinberg.Whether you’re a true road warrior or a slightly less frequent flyer, picking a single airline can be a great way to earn bonus miles and other perks if you’re able to qualify for elite status. TPG reader Eric wants to know whether he should make this decision based on the points he already has or the other way around….[pullquote source=“TPG READER ERIC”]I’m not currently loyal to a single airline but if I were to choose one it would probably be American Airlines since my home airport is DCA. However, most of my points are Amex Membership Rewards points. Is there an airline that works better with Amex points?[/pullquote]At first glance, the simple answer to this question is, “Yes.” The three major credit card issuers (American Express, Citi and Chase) each partner with one of the major legacy carriers in the US. For Chase, it’s United, with the United Explorer Card and the ability to transfer your Ultimate Rewards points to United MileagePlus at a 1:1 ratio. Citi works closely with American, issuing three of the carrier’s cobranded cards, including the Citi® / AAdvantage® Platinum Select® World Elite Mastercard®. Finally, American Express issues a variety of Delta cobranded cards and allows 1:1 point transfers from Membership Rewards to Delta SkyMiles.The information for the Citi AAdvantage Platinum card has been collected independently by The Points Guy. The card details on this page have not been reviewed or provided by the card issuer.Sign up for our daily newsletterEmail addressSign upI would like to subscribe to The Points Guy newsletters and special email promotions. The Points Guy will not share or sell your email. See privacy policy.Eric is thus in a tough spot. Even though American Airlines would be an easier choice given his location, his Amex points appear to be more useful with Delta. However, he might be better off keeping his primary airline and credit card issuers separate.Don’t Forget to DiversifyThere’s a strong argument to be made for earning one set of miles from the airline you fly and using a credit card that earns transferable points to diversify into other options. If Eric uses the “Amex trifecta” for most of his spending, he can transfer those points to a plethora of different airlines spread across Star Alliance (Aeroplan, Avianca, Singapore, ANA), SkyTeam (Delta, Air France/KLM, Alitalia, Aeromexico) and even Oneworld (British Airways, Cathay Pacific). This means that Eric could use his Membership Rewards points to book routings on just about any airline in the world, or he could leverage them to book Oneworld flights at better rates than he’d get with American Airlines.JT Genter has compiled an extensive list of 11 times when it’s cheaper to book American-operated flights with British Airways Avios, an option that would be available to Eric with his stash of Amex points. Unfortunately, if he manages to earn elite status with American Airlines, he’d likely not be able to utilize his perks on American flights booked with Avios, so he’d want to keep that in mind.Finally, he can rack up his points much faster if he books his airfare with The Platinum Card® from American Express and earns 5x points (on airfare booked directly with the airline or Amex Travel; up to $500,000 on these purchases per calendar year), as opposed to 2x miles if he booked with an American Airlines credit card.Bottom LineEric is not wrong to look for a synergistic pairing of airline loyalty and credit cards, but unfortunately American Airlines is the only one of the three US legacy carriers where this isn’t really possible. Instead, he should jump at this chance to diversify his points earning by taking advantage of transferable points cards that can be used to book flights across all three major alliances, and even to book flights on American Airlines for less miles than the AAdvantage program charges.Thanks for the question, Eric, and if you’re a TPG reader who’d like us to answer a question of your own, tweet us at @thepointsguy, message us on Facebook or email us at info@thepointsguy.com.