Earn three points for every dollar in interest you accrue on your monthly balances. Obviously its never good for someone to have a balance but if you do this may be the best card.
http://www.commercebank.com/personal/cards/credit/special-connections-rewards/
HT:http://theforwardcabin.boardingarea.com/2015/06/09/a-credit-card-that-rewards-you-on-interest/
There are tons of cards with 0% apr for the first year or even longer, many with bonuses. These are easily churnable. You also have to know what is the interest rate they are giving you. It's very likely you can find a card with a lower rate even after the 3% is taken into account.