Department store cards are great when you get 10% off all purchases on the day you sign up for the card.
After that… watch out!
You should expect to pay 18-21% on interest rates with department stores. Often that number is far higher than many credit cards.
That 10% only goes so far, and if you do not pay it off, expect to pay 18% or more on future bills. If you have a 6-15% APR credit card, choose that over the 10% discount.