which was the best option after my btech (mech) either MS or Mtech ???

Which course student should go for totally depends on his/her interest and potential and both the courses which you have mentioned above are good and has good scope as well. But as per my view, I would suggest you to choose M.Tech through Gate as this would be the best choice for your career. Also, if you clear Gate exam then this would be giving you an opportunity to get admission in higher studies i.e. M.Tech/M.E or you can also get recruited in PSUs like IOCL, BHEL, ONGC,BSNL etc but the only condition is you will have to get really good score to get admission or recruitment in the same. Apart from this, you can check the scope of M.Tech in Mechanical below and accordingly you can decide -

Mechanical Engineering is one of the oldest branch in engineering, another remarkable advantage of Mechanical Engineering is that its scope is everlasting. And masters in mechanical engineering can get career placements in almost every sector, from steel industry to automobile and from construction to software. Also, it has a wide scope of jobs in public, private and abroad as well like -

Private Sector - You can get job in major mechanical companies in India such as: Siemens, Indian Oil, Tata Motors, Larsen and Toubro, Mahindra & Mahindra, Toshiba and Reliance Industries etc, Major industries in private sector suitable for M. Tech. degree holder in mechanical engineering are: Automobile, Power & Energy, Oil & Gas, Chemical and Construction etc, you can also work in logistics & auto engineering firms as consultant.

Government Sector - A Government sector job is considered more safe & secure in comparison to private sector jobs, but you have to keep in mind that salaries in Government sector are not as high as in private sector. Some of the popular industries in the Govt. sector are:

Public Sector Undertaking (PSU)

India Defense Services India Railways/Metro Rail

Government Power & Energy Organizations

State Government – Engineering Division

Job Overseas - There are a number of excellent quality mechanical research centers in abroad. One of the top notch firms that hire masters in mechanical engineers is Ford. United States, Japan & Korea are some of the countries where post graduate in mechanical engineering, distinctively specialized in automobile engineering, can find good jobs.

Hope this helps!!!!