If you don’t have any personal preference, choosing MD Gynae at AIIMS Delhi will be better. OBG has good facilities. AIIMS Delhi has excellent monitoring facilities and nursing backup. It witnesses many high-risk pregnancy cases. The department offers services such as minimally invasive surgery, preventive & operative oncology, and general gynecology. 

Other than the traditional academics, the department organizes various CMEs, live workshops, and seminars in all fields. OBG-AIIMS is associated with programs such as WHI (Women’s health initiative) program, HRCC (High-Risk Reproduction Centre), and WHO center for research in Reproduction. 

Among the two you should go for MD Gynaecology. Dermatology at AIIMS Rishikesh is quite new. They have reasonably good facilities, although lasers are currently unavailable, and the patient wards have just been established. 

As for learning in OPD and for various other procedures, it is pretty good, as there are a variety of cases.

As a department, ObGyn at AIIMS Delhi is far ahead of Dermatology at AIIMS Rishikesh. Though the comparison might even be futile as they are quite different from each other.

It will be better if you first give priority to choosing the branch,  as in the end your interest in a particular subject will matter more than choosing either AIIMS Rishikesh or Delhi.