Preparing for the SCJA exam will help you get acquainted with the basic Java-related tools and technologies, especially those related to Java
You cannot gain all of this experience with SCJP only. Also, the SCJP exam is quite difficult, so taking the easier SCJA exam will get you familair with the test
The SCJP can take 6 month to a year of experience and studying to pass. You can pass the SCJA after two months of studying with no previous Java experience.
I would take the SCJA followed by the SCJP.
Good luck with whatever path you decided to follow.