The best card for your situation will depend on your travel profile, spending priorities, and whether you can use the offered benefits.
The comparison of these cards is unique because the Amex Platinum card comes with the ability to transfer Membership Rewards points to Delta, allows you to purchase flights on Delta and earn SkyMiles, and has complimentary access to the Delta Sky Club.
The Amex Platinum card can be a better card for the frequent international traveler who is already a Medallion elite member and receives core Delta benefits through elite status.
If a traveler flies predominantly domestically with Delta and will not use the international lounge benefits or other Amex Platinum card benefits, the Delta Reserve card could deliver more bottom-line value.