I personally prefer doing MBA after getting 2-3+ years of experience. Doing MBA right after B.Tech or after getting experience won't make much difference. But it is good to get knowledge about the industry, know the work culture and then do MBA. But some people can not concentrate on studying after getting into a job. So it depends on you. If you can concentrate on studying after working, then I suggest you do MBA after getting some experience. And if you think you can't concentrate, then you can do MBA right after B.Tech.