The rate for a home improvement personal loan is fixed, and credit card interest rates are variable, so using the loan usually results in less interest to pay. An exception might be if you have a card with an introductory interest rate that is lower than the home improvement loan rate. In that case, using your credit card might be better.
Additionally, credit card payments can vary from month to month, making it hard to save money and pay off your debt. Home improvement loans have fixed monthly payments, which means no surprises on how much you owe each month. In either case, remember that you can always pay off the debt early without penalty to save even more.