Both of these colleges have a good reputation and provide great infrastructure and faculty. But, the courses you have mentioned are pretty different. Biotechnology is related to the technology used in enhancing medical and healthcare domain. Mining Engineering explores the technological domain of mining and innovations used in it. So, focus on what your interests and which syllabus will be better for you. However, NIT Warangal is better in rankings compared to NIT Nagpur. But, in the end your course will matter more because you will meet like-minded people in your course and your college life will be better.