Definitely do the SCJP 1.5 exam. Java is already at version 1.6, so there's absolutely no good reason to still take the SCJP 1.4. Sure, the SCJP 1.5 is substantially harder, but that's just the learning curve you have to go through to be a Java programmer today.
Besides, imagine what would happen if a prospective employer were to ask you, "Why did you do the SCJP 1.4 instead of 1.5?" Surely you won't want to answer, "Well, I just wanted to do the easier exam..."