The Amex Blue Cash Preferred (if you are looking for a non-travel card) is probably the best for groceries (6% up to a limit of $6,000 total spending) and gas (3%) if you are just looking for an everyday card. The card comes with an annual fee of $95, but easily offset by the first year bonus and in general, if you can max the spending limit. Those who don't spend the 6,000 organically on groceries tend to utilize the card on giftcards for other spending to get the 6% back on other areas of spending like restaurant, Disney GCs, etc.
@wendow has Kroger by her, which offers fuel rewards on top of the 6%, and has been able to maximize the Amex BCP quite well I believe.
Otherwise, there's the Discover IT that acts like the 5% rotating Freedom, but for the first year, they double your cash back, CFU (1.5% on the surface, but if transferred to a CSP/CSR, becomes up to 2.25 when redeemed through the UR portal and possibly more if transferred to a partner) or the Citi DoubleCash (2% outright) which many seem to love who are over 5/24.
Honestly, the best return for everyday spend in this hobby is the sign up bonuses. If you are always working on a minimum spend, the return is almost always at least 10%.