Is it advisable to opt for a dual degree, say at NIT or IIITM Gwalior or IIEST Shibpur, or only B.Tech at the same institutes? Which one gives more pay and jobs?

I would recommend you to go for a B.Tech course rather than a dual degree program if you are expecting to get hired after the completion of your engineering.

Companies prefer candidates who are graduates a little more than post-graduates when it comes to recruitment for jobs. Also, choosing a dual degree program would mean that you will be spending one extra year in rigorous coursework and projects. Projects that are there in the curriculum of Post Graduate Programs can be pretty hectic and could weaken your spirits especially at times when you see your friends graduating and getting job opportunities from companies.

However, if you have plans to spend more time in the academic fields then I would suggest you consider a dual degree for your career. A dual degree can help you a lot in your higher education. If you can qualify for competitive examinations like GATE, then you will be eligible to get a monthly stipend for pursuing M.Tech for 1 year.

The final choice is in your hands as you would have to consider the pros and cons of both the programs. You can perform further research and analysis to make the final decision for your Career.