Hey Prosenjit -
I'd say definitely go for 1.4 and here's why:
1) The 1.2
test is old. It will only be around until 1.4 has been fully integrated around the world. You know the technical world moves quickly, it's easy to be 'yesterday's news', and 1.2 has that feeling. It is yesterday's news. (I'm exaggerating a little bit but it's a little like saying 'I'm certified in Windows 3.1')
2) You can make the argument that 1.4 is actually easier to study for...
a) The 1.4 questions are probably a little harder than the 1.2 questions, but...
b) You don't have to study AWT (which is a BIG topic)
c) You don't have to study I/O (which is also a BIG topic)
d) You have to add assertions (which are easy)
e) You have to add two new collection classes (which are easy)
So the upshot is: Studying for 1.4 is more focused.