To better understand both the colleges i am providing here rating in terms of their performance in various areas this will make your decision easy.

DOON INSTITUTE OF MEDICAL SCIENCE

• Academic - 8
• Faculty - 9
• Accommodation - 9
• Infrastructure - 7
• Placement- 9

COMBINED INSTITUTE OF MEDICAL SCIENCE

• Academic - 8
• Faculty - 9
• Accommodation - 9
• Infrastructure - 9
• Placement- 10

From the above ratings i believe there is slight difference between two of them in terms of placement and infrastructure.you can choose according to your preference.