You must define what you mean better in order to answer this question.
To me, buying with credit cards is virtually always better because my credit cards maximize my wealth (they offer cash-back, they provide security, they delay my payment, and I never pay interest on them). For you it may or may not be better in this sense depending on the discount amount and how much interest you will pay on the additional amount on your credit card.
Better can mean other things as well. If you are a person who is trying to learn to control your spending, then better may mean it's easier to have discipline when using cash. This is certainly true.
You may also have other reasons to think cash is better, like you have a personal aversion to having debt, even if you pay no interest on it. Nothing wrong with that, but it's not a universal value--I don't feel that way.
First you need to decide for yourself what better means for you, then you can evaluate which option satisfies it.
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Credit cards can be very beneficial if you have fiscal discipline, and they can punish you terribly if you do not.
Advantages of Credit Cards
- Convenient to not have to worry about how much money to carry around.
- Credit card rewards. For example
- Cash back--2% is a good amount
- Insurance on certain things you buy with it (like rental cars)
- Price rewind (pays you the difference when you buy something and it later drops in price)
- And many others
- Easy monitoring and managing of your spending (you can always look up how much you have spent this month)
- The credit card company pays for stuff and you don't have to pay them until the end of the following month. You earn a little interest in the mean time. Also if you have a large unexpected expense, you have a month and a half or so to get money to pay for it. Worst case scenario you can carry a balance for a very short time until you can recover.
- If you are defrauded or your card is stolen, the credit card company will eat the loss.
- If you pay off your statement in full within the month after getting it, you pay no interest.
- Having credit cards and paying them off regularly will build your credit and make it easier to get loans for houses and other such things.
Credit cards can be a cruel scourge if you are a person who does not manage your money very well. If you don't pay off your card at the end of the month, you will start paying a lot of interest and you lose your grace period (so that new purchases immediately start incurring interest).
Notice that I am also incredibly averse to debt that charges interest, but if I have a debt that charges no interest and I'm not afraid of my ability to pay it off, I'm all in.
My Advice for You
Pay for everything you can with your credit card (get one with good rewards if you can). Create an account on mint.com and download the app. Check your total credit card balance every time you go to the bathroom. Don't let it get too close to the amount of money you get from your paycheck minus your fixed costs (like rent). Pay all credit cards off at the end of each month. If you have more than a few hundred dollars remaining after paying them off, move the excess into a high-yield long-term savings account that you use for emergencies. If that gets a high balance, then look moving some of it elsewhere, like paying off your mortgage early.
Never use credit cards for long-term borrowing. And of course, don't habitually spend more than you earn.