Unless you are using a very old version of JSP (JSP 1.2 or 1.1 to be exact) you shouldn't be using either of those. Those are JSTL 1.0 URIs and are not suited to modern versions of JSP.
The two libraries differed in that one would allow run-time expressions as tag attribute values, and one wouldn't. In modern JSP and JSTL, where the JSP engine does all expression evaluation, it's no longer relevant.