My friend got selected in all the 3 institutes; KGMU, IMS BHU, and AIIMS Rishikesh but chose KGMU as her first preference. She had no personal grudge against AIIMS Rishikesh but there were quite a few reasons why she did not choose IMS BHU
However, her decision of choosing one over the other was solely influenced by her personal inclinations. She did not find any major differences except the rural service bond which she was ready to sacrifice. She did not give much thought to AIIMS Rishikesh as it was a new institute at that time although it has grown exponentially over the years so you can give it preference too.
Ultimately, there is no major difference in each of these institutes academically and it is all based on your personal indications.