Impersonation attacks involve the penetration tester assuming the identity of a valid user to gain unauthorized access to systems or information. This method is particularly effective for gathering valid user credentials, as it can involve tactics such as phishing, social engineering, or exploiting weak authentication processes. The other options, such as Wardriving, Captive portal, and Deauthentication, are more focused on wireless network vulnerabilities and are less direct in obtaining user credentials.