Welcome to FT!
It might help to know some background info... do you already have substantial miles with a particular FF program? Do you have to or prefer to fly with a specific carrier or alliance?
One general purpose card that is highly recommended (though I don't yet have one myself) is the Starwood Preferred Guest AMEX as it allows transfer of points into several FF programs.
https://www143.americanexpress.com/a...landingCode=74But there are, of course, many others and it can depend upon your specific preferences and needs.