I don't have that much experience when it comes to credit cards.  I'm very wary when it comes to signing up for cards because, lets face it, one false move and there goes your credit!
Capital One Mastercard was my first card.  I had a few problems with the card, in particular the fee posting dates seemed to change whenever they felt like it.  I was assured that the dates didn't change by a member of customer service but, sure enough, month after month they would pick a different day to charge my account.  Another issue is the interest rate.  It was ridiculously high (in the mid twenties on...