This is a fairly common question and also a complicated one to answer. In reality, doing both things will result in denting your credit score. The reason for this is that having many credit cards with outstanding balances will raise red flags but at the same time maxing one out will put you in a precarious position against the credit bureaus. From a credit score perspective the worst you can do is to max a credit score, to put into perspective it is never recommended to exceed the usage of a card in more than 30% at any given time. This is considered to be the rule of thumb on how to get the max out of a card without getting into territory that would otherwise affect your credit score.