I'm primarily using a Discover Miles card that they don't offer anymore. $60 annual fee, but straight 2% on everything (assuming you use it for either travel credit or Amazon). I also have an Amazon card for the 3% at Amazon and a Costco card that does 4% on gas, 3% on restaurants, 2% at Costco, and 1% for everything else, but the rewards are only redeemable at Costco.
If people aren't aware of it, Nerdwallet is a fantastic resource for evaluating rewards cards. They have a calculator that lets you tell it roughly how much you spend on various categories each month, and it'll give you suggestions on which cards will net you the most in rewards.
https://www.nerdwallet.com/credit-cards