re: How to maximize credit card rewards

If you are only planning on flying Delta, the DL Amex gold/platinum/reserve cards are all fine and will benefit you in different ways. You receive miles when using these cards and not points. The miles are redeemed through Delta and different routes cost more than others. The DL platinum and reserve cards offer MQM bonuses when you reach a certain spend which are very helpful in maintaining or bumping to a higher status.They also offer companion certificates and the Reserve access to the skyclub.

Typically you get the most bang for your points when DL offers different award sales. It is truly random.

The regular Platinum Amex will also benefit you as you can access the DL Skyclub (your wife will not get free access). It has a separate points system than the DL credit cards. The Chase Sapphire Reserve does not have any DL specific perks however it is a helpful card to any traveler.