Best practices when creating SQL based SmartObjects?

It appears there are two ways to join data from two SQL tables in SmartObjects. You can either create a List method in a single SmartObject that calls two List Service Object methods and "join" them by specifying a link between them, or you can create two SmartObjects, one for each List Service Object method and "join" them by creating an assocation between the two SmartObjects. Is there a best practice, or reason for choosing one method over another? It appears that if you want to do master/child editing in SmartForms, then the latter approach is the way to go? Anyone have any insight or recommendations?