Well, if you are interested in Grocery Store & Gas Station purchases, you should check this chart and select the cards that best match your spending. For most people, that would be the Sallie Mae card.
https://www.salliemae.com/credit-cards/sallie-mae-card/
Otherwise, a good non-category specific card can be useful, to make sure you are getting at least 2% or 1.5% cash back on all purchases. Citi Double Cash seems popular, unless you want to try for the NASA card. And the Bank of America Better Balance Rewards is pretty good, you don't need to use it very much, and you can get $100 a year cash back ($120 if you have a BOA Checking or Savings account). Some people have 3 or 4 Better Balance rewards cards... Very few people have the JCB Marukai card, but if you can get it, its almost 3% cash back on everything.
If you have more specific spending categories, we can provide more assistance.
