Howdy Pradeep!
Welcome to the Ranch!
About which exam:
The 1.5 is newer than the 1.4, so it is better to take the 1.5 in my opinion.
Some difficult topics are new to the 1.5 especially a lot of generics that takes some time.
But the 1.4 has also a lot on the Math class and bitshifting that will not appear on 1.5.
To start with, get the K&B book first before you buy exam software like withlabs. There are also some free mock exams on the net.
Get the book, study, write a lot of code, perhaps make up your own little question catalogue. Then go for the free mocks, and when you are still uncertain, you may think about getting the whizlabs software.
Perhaps have a look at out FAQ page:
http://faq.javaranch.com/view?ScjpFaq especially where the free mock exams can be found:
http://faq.javaranch.com/view?ScjpFaq#mocks Good luck!
Yours,
Bu.