If you have an average-sized or big family, for instance, there are several cash back cards that offers some highly-competitive cash back percentages on categories such as supermarket spending, department-store and gas-station purchases. Chances are, you spend a fortune in supermarkets and department stores. And you probably have to top up your gas tank regularly, what with you being an unpaid taxi driver for your kids.
If you're young, single, don't have a car, always eat out, and wouldn't be seen dead in a department store, then rewards in those categories would be a very poor pick for you.
Airline credit cards
The same applies with other sorts of plastic. Of course, few people with a morbid fear of flying have airline credit cards. That would be too silly. But quite a lot more probably have one when they don't need it. Unless you take to the air frequently and so earn lots of miles at premium rates, what's the point in earning 1-percent rewards on "other purchases" on an airline card when you could be earning 3 percent or more on a general one?
Of course, if you're a frequent flier, airline credit cards can be very rewarding. But you still have to ask yourself which card is best for you. For example, you can often trade off a higher annual fee for better rewards and privileges, including accessing lounges and cutting airport lines. There is no objective, empirically correct answer to these sorts of issues. If you're a Spartan sort who greets discomfort with steely stoicism, then no number of perks is going to see you part with a cent. But if you're the ultimate, self-indulgent diva -- or divus, if you're a male Latin scholar* -- then you might well be prepared to pay three-figure annual fees, even if you rarely fly, in order to make your trips more comfortable.