Hi,

All of them are good colleges for pursuing MBBS. NRS and RG kar are good but my humble suggestion is go for IPGMER as the institute have better rating compared to other two. It is a suggestion only because in the end it depends on the performance of students. All three of them are best ones. You can also compare the colleges of your choices and choose the best for you by using college comparing tool

https://www.careers360.com/compare-colleges

All the best.