The first question to answer is what kind of rewards are you interested in? Do you want flights, hotel points, or cash?

The second question is how much do you spend a month, and on what? Do you spend a lot on travel, or restaurants, or does it just tend to be groceries and gas?

After you answer those questions, we can provide better suggestions.

In my opinion, with the airlines devaluing their points year after year, getting miles from credit cards no longer makes sense for most people. Unless you fly a lot (particularly internationally or in premium cabins) cash back is probably the way to go, but it depends on your habits/goals.