It's better to always have a paid off balance on your credit card which will help improve your credit score.
Carrying a balance on your credit card won't harm your credit but your credit rating will improve if you always pay off the balance you owe on your credit card in full.
Try to keep your credit card balance to a minimum and the more of the balance on your credit card you have paid off the better your credit rating will be since it shows you're good at paying off your credit card balances.