Depending on the types of cards you will accept, there are several different choices for type of merchant account depending on the types of cards you will accept. Most businesses use third party processors referred to them by their own bank or credit card company.
Both MasterCard and Visa require that a business use a third party provider. Some credit card companies, like American Express and Discover, provide credit card processing services themselves. For these reasons, it is a good idea to evaluate your credit card needs before seeking a merchant account.