Is KGMU better or AIIMS Rishikesh?

Being a central institute is not important, it's about the scope of learning offered at a medical school. 

AIIMS Rishikesh is a central institute, so it has a better administration. However, KGMU offers much more practical knowledge to its students. MBBS is all about gaining practical knowledge. The number and types of patients received by KGMU is very high. As you enter your clinical years, you’ll realize the importance of these things.

AIIMS Faculties are better administered than state faculties. However, MBBS is about your own efforts and approach towards studies. Teachers can only guide you, the hard work is your job entirely. So faculties aren’t much of a concern. Moreover, KGMU also has highly qualified faculties.

I would say KGMU is better than all the other AIIMS, except AIIMS Delhi.