It depends on the card, your lifestyle and the usage you get out of that card. Some cards will offer bonus miles on the anniversary of that card which might be well worth paying the annual fee and then canceling. There are other cards which in my mind have no use other than a quick 35K-50K miles which I would never pay an annual fee for.

There are also some cards you might feel worth keeping them open due to your lifestyle. I personally like having the Chase Ink Bold open just because its a great card to put utilities and gas on each month in order to maximize points in those categories and the Chase Sapphire just because I eat out a lot and can get double points at restaurants. Both have other benefits that might be a positive or negative to your lifestyle but that is just an example.

Just look at your spending habits and see if any of the cards you have fit your lifestyle and create your own philosophy from there. Everyone on this board is different so there is no right or wrong card to keep or cancel. Just do what you think would maximize miles for your own particular situation.