First, if you don't use a credit card for absolutely every single purchase you can, you're making a huge mistake. Even if it is just a penny per purchase, it is superior to nothing per purchase.
Now, with that being said, what credit cars do you guys use, or recommend? I'm currently using the combo of the Chase Freedom card with the Chase Sapphire Preferred for the bonuses. That 40,000 point bonus bought me half a ticket to Europe right from the start