Ask yourself which version of
J2EE are you most comfortable with? Since there is a lot of changes between J2EE 1.2 (which is used for the current SCEA exam) and JEE5 (that will be used for the SCEA 5 version of the exam), you need to figure out where your comfort zone is.
Granted the newer exam will probably be more relevant in today's market, but hey a SCEA is SCEA.. no one really checks which version of SCEA you are
If you have a need to get certified soon, then take the existing version of the exam. In all reality, the existing version will probably a little easier since there is are a lot of books/training material available.
If you are not planning to take the exam for the next 6 months or so, then my recommendation is that you wait for the SCEA 5 version of the exam. Give time for books/training material to come out.
Mark Cade's new book on SCEA was supposed to come out earlier in 2007 (updated for J2EE 1.4), but it has been pushed back till 05/2008. (I am guessing it is because the book is being revised for SCEA 5?)
Lastly, if you are well versed with JEE5 or don't mind putting in the effort to get up to speed in a short time, take the free SCEA 5 beta exam..
Good luck!