Among RIMS Imphal and NEIGRIHMS Shillong, the latter is a better option. In the northeastern region, it is the first post-graduate medical institute. It is an autonomous institute, which is run by the Ministry of Health and Family Welfare. The faculties at the institute are great. Many guest speakers visit the institute from Delhi. It also has a better patient flow. Although the campus of NEIGRIHMS is smaller as compared to RIMS Imphal, it offers better infrastructure. 

With NEIGRIHMS, you will get a better campus, more one-on-one attention, and a comparably easy undergraduate life. On the other hand, GMCH will offer you better patients, cases, more experienced faculty, and better exposure. Guwahati will also offer better connectivity and opportunities. NEIGRIHMS is still in its initial stages. So, there are certain opportunities that you will only get at GMCH, currently. 

RIMS Imphal is the oldest medical institute in northeast India. NIRF 2021 has ranked the institute 43 for medical sciences. It is also the first choice for most medical aspirants. NEIGRIHMS, Shillong is the second choice for most students since it is a Central Govt. Institute. Due to high fees, AGMC, Agartala is less preferred among students. 

NEIGRIHMS Shillong is the better choice. In fact, it is considered among the top five institutes of excellence. It is a well-resourced premium central Govt. institute. While SNMC Agra is an old state medical college with limited resources. 

However, you should keep in mind that, NEIGRIHMS is located in a remote corner of the country. Whereas, SNMC is located in central India. At NEIGRIHMS, you will get better quality education. But at SNMC, you will get more time to prepare for postgraduate and better working options. 

If you are not from northeast, you can choose SNMC for UG and prepare for better options in PG.