Should I take the 1.2 or 1.4 exam?

The SCJP 1.2 is quite an old exam. It is for people who are still working with Java 1.2 platform, and you are very unlikely to come across a Java 1.2 project. So I would really recommend you to go for the SCJP 1.4 exam. Here is what Sun says about SCJP 1.2 and SCJP 1.4

What are the differences between Sun Certified Programmer for Java 2 Platform 1.2 (CX-310-025) and 1.4 (CX-310-035) exams?

• All AWT objectives have been removed (there are no questions on GUI programming).
• All I/O objectives have been removed.
• An objective on Assertions has been added.
• A few of the previous objectives have been strengthened (you can expect more/more detailed questions of them). They include: hashcode and equals, Collections, Wrapper classes.

What has been removed from the new programmer 1.4 exam?

• All objectives related to AWT (there will be no questions on GUI programming.
• All objectives related to I/O.

What has been added to the new programmer 1.4 exam?

• Questions on the Assertion mechanism will be on the exam (you must know how to appropriately use assertions (for example, not just how but when) and you must know the command-line switches for both compiling and running with assertions enabled).
• Questions on Collections, equals, hashcode, and the Wrapper classes have been deepened, so you can expect more detailed questions on these topics.