I tend to pay them in full every month and put a good amount on them each month.
I have one card that I get frequent flyer miles on. With the requirement to have activity on account more regularly than I'm flying that airline lately, this is keeping the frequent flyer account active.
Other than that, lately, I like the cash back. Typically 1%. It isn't much, but adds up, especially when you use it for everyday things AND PAY OFF IN FULL EACH MONTH.
One thing I have that I'm not sure I like much or not.... is cash back, but... it goes towards the mortgage. So, for every $2500 I charge, knock $25 off the mortage...
I do watch for good freebies to signup for new cards, though don't want to have too many, even if they are no fee. I got $250 in GCs to signup for an AmEx business card, w/ no fee for first year. Liked that.... I thought I would use the card more but the one place I wanted it for doesn't accept AmEx so I'm not sure if I'll renew, even if I get another $100 GC to renew.