I look at this once in a while and always come down on getting miles.

I have a 2% cash back card, but, pretty much only use it overseas due to ripoff forex chages on Amex and other, miles earning, Visa and MC.

To me, an F ticket to, say Hong Kong, is worth more than three thousand bucks which is what I might get back if I used the 2% card instead of getting miles. Plus, I leverage my spend by getting large credit card bonuses (thanks fellow FTers ) which I can't get on cash back cards.