Hi Dhanalakshmi,
After accomplishing MBBS for every PG aspirant prefers medicine the most. There are  plenty of seats available in DNB and most of them are likely to be good for medicine. In the field of medicine, every new case enhances your experience , so you essentially require a well maintained and quality OPD and IPD.

Bed Capacity in hospital, ICU's, ICCU's always matters and they directly indicate  the exposure you will be experiencing in that particular hospital. Government and Private both the Hospitals are good only when they have a good number of beds which can empower your skills with the every new case you associate.

The below are few good hospitals for DNB Medicine are as follows:
1) Sir Gangaram Hospital, Del

2) lLilavati Hospital and Research Centre, Bandra, Mumbai
3)Balabhai Nanavati Hospital S.V. Road, Vile Parle (West), Mumbai
4) Lisie Hospital, Ernakulam, Kerala
5) Lourde Hospital Road, Ernakulam, Kerala
6)Narayana Hrudayalaya of Bangalore
7)Marthas Hospital, Nrupathunga Road, Bangalore
8)Breach Candy Hospital, Mumbai
9)Hinduja, Mumbai
10)Madurai Meenakshi Mission Hospital, Madurai, Tamil Nadu
11)Pushpagiri Hospital, Tiruvella, Kerala