From the perspective of job opportunities it does not matter whether you are a B Tech or an M Tech in most case. However, if you want to improve your CV in terms of where you have studied from, then you could go for an M Tech. What I am trying to convey is that if you did your B Tech from a not very highly rated college and you get a good score in GATE and get entrance to IIT like college then you could opt to go for M Tech and improve your job prospects.
If you are financially strong and you have no need a job yet then must go for further studies like M. Tech or MBA otherwise you can do a job and complete you study through correspondence also. Best of luck!