I think you should study for 1.4. It is really not all that different from 1.3. I would say that JSTL and EL (the expression language) are the biggest additions that the 1.4 test has. People say that 1.4 is harder. I didn't find it to be more difficult, personally. Even though a lot of companies are still using J2EE 1.3, it is still good to know JSTL because you can use the 1.0 version of JSTL with JSP 1.2. You might as well show potential employers that you are up to date on the latest technologies and go with the 1.4 test. Hope that helped.
i agree to what Anthony says. It is really not all that different from 1.3(especially the servlet stuff). Moreover, there seems to be a bit of *fuss* about 1.4. (Partially justifiable, though) But JSTL/EL are easy and interesting to learn. So, if time is not a real constraint, one should go for 1.4. It is always better to stay updated.
To know recursion, you must first know recursion...