All three insulations, AIIMS Patna, KGMC Lucknow, and Grant Medical College, Mumbai, are well-respected in the field of medicine and have a strong reputation for providing quality education and training to students pursuing an MBBS degree.

AIIMS Patna is known for its top-notch infrastructure and other campus facilities and good academics. It’s the most preferable AIIMS after Delhi. KGMC Lucknow is also a decent college though I am not aware of its infrastructure. GGMC Mumbai on the other hand is the best option of the three. Here is why 

• Its prime location plays a big role in making it the better option of the 3 institutes. Mumbai is a much more preferred city than Lucknow or Patna.
• The patient inflow is diverse and huge enabling you to witness a variety of cases both common and rare in your UG itself.
• Academic-wise too, this institute gives an edge over other institutes. With a well-structured curriculum and highly qualified professors, you will get an amazing learning experience 
• Great emphasis is given to the attendance and practicals of every subject.
• In addition to academics, this college is well known for its active extracurricular culture. It has its own Gymkhana at Marine drives in addition to various cultural, and sports events and quizzes.
• The hostel facilities are also decent as per government standards.
• There are around 3-4 canteens and food served here is at subsidized rates.

The above list is not exhaustive and there are many more points as to why GGMC is a better choice than AIIMS Patna and KGMC Lucknow. Ultimately, it’s your call to make. If you are after the AIIMS tag, go for AIIMS Patna but if you want to enjoy your life along with decent academics then JJ would be the best choice for you.

Without any second thoughts, go for UCMS. The academic ambiance is almost the same at both the colleges and both of them are highly reputed. Here are a few additional benefits of choosing UCMS over KGMU

1. You will not have to go through the rural bond
2. Generally, colleges in Delhi are far better than the colleges in UP. So as 50% of seats in NEET are reserved for State counseling admission to UCMS will be far easier.
3. Under the UP system, extra merit is given to those who have worked in PHCs for state counseling making it difficult for a fresher. Delhi doesn’t have such a policy.
4. Life outside campus is fun both in Delhi and Lucknow. Lucknow is known to have excellent food places while Delhi is the capital city. 
5. UCMS allows its students to attend the festival of various other Delhi colleges including AIIMS's Pulse.

Overall, both colleges have their strengths and weaknesses so choose wisely!

KGMU was established as early as 1905 while AIIMS Patna was established recently in 202. So the former seems to be more experienced with better opportunities and senior faculties. Let's look at these institutes one to one for a better understanding.

KGMC is one of the prominent colleges in north India and is preferred to many colleges in Delhi. The students here are called georgians

KGMC

• The clinical exposure offered here is unmatched and it produces many skilled doctors.
• It enjoys a central location of being in the capital city of UP.
• KGMC has an extensive alumni base that has made significant contributions to society.
• The 2 major flaws of KGMC are its huge batch size and the bond after MBBS.
• KGMU has 50% reservation in PG in the state quota.
• It receives the maximum number of serious cases of North East India 
• The institute boasts excellent infrastructure.
• Despite it being old, it is equipped with maximum medical instruments and is well-maintained.

AIIMS Patna

• It's far off from the main city and thus its location might be disadvantageous to some.
• It's relatively new and thus lacks good alumni.
• AIIMS Patna has many better and high-quality hostel and mess facilities that aren't available in KGMC.
• The quality of education offered at AIIMS Patna is top notch
• The student body is more diverse, as the seats are filled from AIQ 100%. 
• It also focuses on extracurricular in addition to the excellent academic environment and students are given a chance to explore their passions and develop as a whole.
• No 50% reservation for PG here

All in all, considering the AIIMS tag and the fast-paced growth the institute has witnessed, AIIMS Patna is the best choice for you.

The hostel facilities of IMS BHU and KGMU are at par with each other with no major differences. Here are the year-wise hostels allotted to students of both colleges 

First-year:

• BHU : First-year students of BHU are allotted the Punarvasu Atreya Hostel. This is the hostel with the best facility wherein students are offered double occupancy rooms. There are some restrictions in the initial months. The mess food in this hostel is decent and it also has a small play area. Other facilities include 24-hour electricity and water supply with free internet wifi. 
• KGMU : KGMU first-year students are allotted the CV hostel that has double occupancy rooms. It has Wi-Fi availability, scenery mess food, and a canteen, but is slightly larger than the Atreus hostel of BHU 

So, for the first-year students, KGMU hostel > IMS BHU hostel

Second Year

• IMS BHU: The second-year students of IMS BHU are allotted the Ruiya hostel which is the most beautiful hostel of IMS BHU. It’s known for its lush greenery and is widely spread in a huge area. The rooms are triple occupancy.
• KGMU: The second-year students are allotted to the TG hostel which is a multistorey building situated in a colony. Single occupancy rooms are allotted to every student. The only drawback is that it’s quite far away from the main campus.

So for the second year, IMS BHU hostel >KGMU

Third year and Last year:

• IMS BHU : The third-year students of IMS BHU are allotted the Ruiya annex hostel which is very well furnished with double occupancy rooms. In the last year, students have been allotted the Dhanvantari hostel which has single occupancy rooms.
• KGMU: The third and last-year students of KGMU are allotted with SP hostel which has double occupancy rooms. If you score good marks in your final year, then you may get a single-room

So for third-year hostels, IMS BHU ~KGMU

Overall, the hostels of both IMS BHU and KGMU are equally good in terms of cleanliness and maintenance.

Many people consider IMS BHU better than KGMU due to internal PG. But the truth is internal PG at IMS BHU will only give only a single attempt to get an internal seat at a low rank. Moreover, owing to the rotation system in a particular year, there might be no internal seat for a particular branch for a specific category. If you happen to belong to that particular branch, you will have to be among toppers else you won't be eligible for internal benefit or state quota. KGMU on the other hand, will give you unlimited attempts with a state quota

Also, I feel MBBS is not just about PG, but also about the holistic development of the students. That being said, the IMS tag isn't as valuable as the KGMU tag.

So, I don't think it's wise to choose IMS BHU over KGMU. 

Both are equally good when it comes to resources or rankings. But, KGMC is slightly better in the number and extent of cases. It is also quite ahead of SMS Jaipur reputation-wise. It is on the way to becoming one of the top autonomous medical institutions of excellence. It is ranked 10th for medical by NIRF 2020. SMS Jaipur is ranked 27 in NIRF 20.

You can even compare the paygrade here to AIIMS. The only other comparable college is AIIMS to KGMC.

I have a few friends at KGMC and they vouch for the college. Based on the interactions I had with them, I will suggest that you choose KGMC.