Hello Vikrant,

According to me, this solely depends on your interests. GATE is a very prestigious exam and you can apply to various PSU through your GATE score, such as BHAIL, GAIL, IOC, SAIL. These organisation have a very good reputation and are considered as dream companies by some people. Therefore, applying to any of these companies might be a good option. 

Doing M.Tech is also a good choice provided you do it in a reputed college such as IIT or NIT. 

The same is the case with Ph.D. It is only that your opportunities will increase after having post-graduation. 

Therefore it entirely depends on your interests, gate score. You may consider applying for MS as the gate score can also be used for study abroad scholarships.

Hope this helps

Regards