The simplest answer is, “It doesn’t matter”.
If the parameter in your controller method is of the enumeration type
public IHttpActionResult Foo(RuleType ruleType)
In WebAPI, It Just Works – no matter if the client request URL specifies the parmeter value as ?ruleType=1 or ?ruleType=EmailAddress
If the client specifies a value that isn’t valid for the enumeration, an exception is thrown (The parameters dictionary contains a null entry for parameter 'ruleType' of non-nullable type 'RuleType' for method 'Foo' ... and the client gets a 400 Bad Request response.