In selecting a short form, the difference is instrument length.  The reliability and precision of the short forms within a domain is highly similar.  If you are working in a sample in which you expected huge variability in a domain area and wanted different subdomains covered, you would probably go for the original short form.  If you are working with a sample in which you wanted the most precise measure, you would go for an 8a short form.  If you had little room for additional measures but really wanted to capture something as a secondary outcome, you would go for a 4a short form.