If you search this forum you will find thousands of such discussions. Look at the " I am taking the
SCJP 1.4 " " I am taking the SCJP 1.5 " threads started by Bert to get an idea of why people choose 1.5 or 1.4. 1.5 is harder. You have to learn more features. You can also go though the sun site to know the difference in the syllabus for both these exams.