Both are AIIMS 2012 graduates and are roughly comparable. In terms of research, there are numerous opportunities at AIIMS Raipur. The academic section promotes research on a proactive basis. It has the same facilities and receives the same funding. Every batch has a few people studying for the USMLE.

AIIMS Raipur is only 10-15 minutes from the city center, and there is plenty of development all around it, including all the markets, shops, and restaurants you could want. It all depends on your preferences; if you want to be in and around a city, Raipur is the way to go. 

Rishikesh is a good option if you want to study in a natural and beautiful setting.

At the end of the day, both are excellent institutes that would give you a slight advantage in terms of brand value.