Which is better for mechanical: DTU or IIT (ISM) Dhanbad?

You should choose the college closer to your home. Both the colleges DTU and IIT Dhanbad are Tier-1 engineering colleges in India. 

Degree Outcome:

• Most of the students from these popular Indian colleges practice coding irrespective of their branch and become Computer engineers depending on their skills. 
• The companies visiting for placements do not give much importance to the academic credentials of the candidate as they are only concerned about the TopCoder and GitHub profiles in the applicant’s resume. The salary packages offered by these companies range between 5-50 LPA (depending on the skill of the applicant).
• Many students also become managers in various industries based on their hard work, luck, and personal learning. The companies mainly focus on the previous academic credential of the candidate. The salary packages offered for managerial positions to the students is between 5-15 LPA.

Given below is an overview of both the colleges.

The more well-grounded and genuine way to become a Mechanical or Automobile Engineer in India is to become proficient in the GATE/ IES ME curriculum and participate in some competitive exams to secure a job in the government sector. 

Mechanical engineering is getting outdated and people are not getting in any good place in India by doing Mechanical engineering. This program is even getting shut in various developed countries. So, choose wisely.