It's a basic financial question that many consumers don't consider.
"Maybe one day I'll wish I'd thought more about it," said Lisa Margul, who uses a traditional bank.
Financial experts say credit unions often have better deals because they are owned by their members.
"They're not looking to turn a profit for shareholders," said Todd Mark, of Consumer Credit Counseling Service in Dallas. "It's going back to you as a member."
According to Datatrac, which tracks average bank and credit union interest rates, credit unions routinely beat banks.
They offer lower rates for borrowers and higher rates for savers.
The differences may seem small, but Mark said they can add up.
"It's definitely worth it, especially if you're looking to make a big purchase," he said.
But banks have at least one major advantage over credit unions: convenience.
Banks typically have far more branches and ATMs.
"I don't have to be scheduling my life around the one place that I can bank at," Margul said.
Credit unions must also be joined. But most people can find a credit union where they qualify for membership, Mark said.
After considering the pros and cons of credit unions and banks, many consumers decide the best option is to use both.