AIIMS is definitely the better option. There are many reasons why it is the superior choice. One of them is the competition. You will be competing with lakhs of students to get selected. This entrance examination is trickier than all other entrances. Irrespective of how well-prepared you are, you are likely to get stuck between choices in the examination. 

PGIMER has a standard examination pattern. They usually aim to test how thorough you are. Also, the competition is much less. Since around 15000 or fewer people appear in the examinations. 

Among AIIMS and PGIMER, the latter is comparably better. The experience and exposure you will get there are unmatched. 

AIIMS has a tendency to refer simple or non-interesting cases to Safdarjung, so students don’t get the chance to see all types of cases. PGI on the other hand is not a referral medical center. So, residents can see all types of cases from simple to complicated. 

Although owing to its location, AIIMS offers better training platforms for residents to take off.