You'll find lots of helpful information in the SCJP FAQ
. In my opinion, the answer to your question will depend on your certification goals. If your primary aim is to get one of the "higher" Sun certifications (SCBCD/SCWCD/etc), then I suppose it doesn't quite matter so much which SCJP version you take, since any of them will qualify you to take the higher exams.
But if you're interested in getting some value out of the SCJP itself, then you definitely want to take either the SCJP 1.6 or 1.5 instead of 1.4. Many important new language features were added in Java 1.5, and you'll probably need to learn them for your job anyway, so a SCJP 1.5 certification is undoubtedly more valuable than 1.4 as far as your own skills development is concerned. Also, Java 1.4 is rather outdated by now (the current version is 1.6), and the whole point of certification is to demonstrate your mastery of the latest technology in the market. If I were an interviewer, I would definitely question why you chose to take the SCJP 1.4 when more recent exams have been available for well over two years. (And I would look unfavorably on those who reply that they chose the SCJP 1.4 because it's easier!)