The quality of the designs you receive from both freelancers and creative agencies will vary to a considerable extent. Always make sure to check any agency or freelancers portfolio to see if you like the work they’ve done. In the web design world the size of the business has no correlation to the quality of the work delivered. Some large website design firms have horrible portfolios.
The quality you receive from either o freelancer or an agency depends highly on the nature of the organization or the individual. It is definitely possible to find a freelancer designer who will deliver a higher quality website at a lower cost than a large company or organization.