I would like to know whether a M.tech course from IIT or a MS from US is a better option?

IIT is a premier institute in India and hence it will definitely offer you excellent prospects. However, given an option between the two, a MS from a good university in the US will definitely offer you better prospects. This is mainly due to the fact that the American education is more application oriented and hence you will be easily exposed to a number of methodologies that are developed internationally. Moreover the international exposure that you will receive in an increasingly globalized economy will help you to garner the right skills needed in a global market. It will also give you the option of earning a dollar salary. The decision finally rests with you.