RE: Difference between knowledgebase and knowledge article?
If you are starting a new implementation, I see no reason to use the old entity, as it will probably be deprecated at some point in the future, and I don't see any significant benefits over the new entity.
If you have an existing implementation with the old entity, then the decision is not so easy. If some of the new features (e.g. versioning or translation) are useful, then I'd move to the new entity, but if you're happy with the functionality of the old entity there's not a compelling reason to migrate