Hello Ramesh,

From my experiences, Adwords Keyword Tool is the best keyword research you can get for free. You can start getting valuable keywords with this tool and then develop (adding more or lose more) your keywords by actually test them in google or other search engine machine. You will then know for sure, which ones is favorable to google and which one for the others.

In my opinion there is no other way to know which keyword is the best for your campaign unless you test it and test it and test it again.