I doubt if there is a single book that would qualify for the best study guide. Given the breadth of areas covered, and that the
test comprises of three parts, and that SCEA books are being published only recently makes it even more difficult to define what constitutes "best".
I found study notes, links(from our own SCEA links page) and a few popular titles on each of the covered topics(
EJB, JMS,
Servlets&
JSP, UML, Security etc. ) are necessary and sufficient to prepare for the test.