The difference between a credit union and a bank is the ownership. Credit unions are non-profit cooperatives owned by their members, while banks are for-profit entities. They are also insured by different federal agencies; credit unions are insured by the NCUSIF and banks are insured by the FDIC.
Banks and credit unions offer comparable services, and which is better depends on the consumer and the bank or credit union in question. While credit unions are able to closely tailor their services for the local community, banks are able to take advantage of economies of scale due to their larger size and are more likely to have robust online services.
Members of credit unions vote for board members, and each member has one vote no matter how much or how little is invested in the credit union. Some banks are publicly traded companies and allow shareholders to vote; as with any publicly traded company, the vote is proportional to the value of the shares owned. Having more voice in how the organization operates is an advantage to using a credit union.
Credit unions are required by law to limit their membership to people who have a common bond. The most common membership restrictions for credit unions are geographical location, a particular employer or an association with a particular college or university. Unrestricted membership is an advantage to using a bank; a customer does not have to meet the same membership criteria to open a bank account.