Reading old articles may direct you off into research areas which have been subsequently resolved. More recent articles may contain historical reviews of a field which subsumes and generalises the issues discussed in older articles. Refereed is much better than unreferred . Note that tech reports are usually not refereed and web pages are never refereed. Journals are forums for storing finished products.
Workshops report new and formative ideas.
Conferences are a half-way point between workshops and journals. Typically, authors take their good conference papers, expand them, and turn them into journal articles. Conference is better than workshop. But don't ignore workshops. International publications are better than national.