My opinion is just opposite to Mr mrogers,here is the reason:
1.Data dictionary is tenant aware,so if you save your configuration data in dictionary you don't need do anything,it is just for the tenant.But Attribute service is not tenant aware,If you want to save configruation in attribute ,you should take care of tenant yourself( for example add tenant to attribute key).
2.Using data dictionary give you better extensibility,you can save an xml file in every tenant's data dictionay.When you have others tenant related config property,you just add it to the xml file,then every thing will be ok.