If you are a Sam's Club Business Plus or Advantage Plus member, look at the Sam's Club Discover or Business Discover. No annual fee, and gives up to 2% cash back.
https://www.onlinecreditcenter2.com/...US_DualApp.pdf
SAM’S CLUB ADVANTAGE PLUS MEMBERS
Amount of Year-to-Date Purchases Percentage of Purchase
(including the current Purchase) Eligible for Rebate
Upto $1,500 0.25%
$1,500.01 - $3,000 0.50%
$3,000.01 - $5,000 1.00%
$5,000.01 - $10,000 1.75%
$10,000.01 - $1,000,000 2.00%
With your current level of spending of $550/mo, this card would earn less than 1% overall, but if your Amex spend is significant and you change some of your Amex spend to this card, it may have a better return than what your Delta miles are worth, depending on your flying habits.