Which WSDL should an architect consider when creating an integration that might be used for...

The Partner WSDL is the best option for creating an integration that might be used for more than one Salesforce organization and different metadata.The Partner WSDL is loosely typed and can reflect against any configuration of Salesforce. It is static and does not change if modifications are made to an organization’s Salesforce configuration. Therefore, it is more flexible and adaptable than the Enterprise WSDL, which is strongly typed and bound to a specific configuration of Salesforce1

References: Differences between Salesforce provided WSDL files