<prompt> Human: My thinking is that cash back is liquid, while miles force you to use a particular airline which might have a higher cost. With cash back I can use my rewards to spend at any airline.To expand on my personal experience: I earn somewhere in the range of 3 cash back average annually. My Fidelity AMEX card gives me 2 on everything, and I have a Discover and Chase Freedom card which I use to get 5 on rotating categories. So in order for something like Delta Skymiles to work for me, I would need to be earning more than 3, right?Does anyone here use an airline card? Is it worth it? How do you work it to get maximum value?  <response>: Its only worth it if you fly with one airline a lot. The best rewards are paired with elite status, which you usually cant get solely through credit card points. Also, airline frequent flyer miles can beare devalued fairly frequently and with little notice, and not all of them accept 1:1 transfers from cards like the Chase Sapphire Preferred. 