Here are some of the top colleges for Diploma in Mechanical Engineering :

1. Advanced Technical Training Centre, Sikkim

2. Yamuna Group of Institutions, Yamuna nagar

3. Swami Vivekananda Institute of Engineering and Technology, Chandigarh

4. ABS Academy of Polytechnic, Durgapur

5. GIST , haldia

6. Lovely Professional University

7. NSHM Knowledge Campus, Durgapur

It is difficult to rank one college as the best for diploma in ME as there is no such official ranking available, however, the ones i mentioned are top in the country for your subject with great faculty and placement options.