I would say take the 1.4 exam. No employer/manager would mind you having a 1.4 cert even if you're going to develop in a 1.2/1.3 environment. The reverse is different though; if you're going to do 1.4 work, then the 1.2 cert looks a bit "old" (is it time for me to consider do some 1.4 exam prep?
).
The only case I would see it making sense to take the 1.2 exam, is that you've studied 1.2 stuff already and well and need the cert NOW. If you have 1-2 months of time then it while worthwhile learning the 1.4 stuff anyway.
Hope this helps,
Panagiotis (SCJP2, 91%, Jan '01)