Whether you should leave Seth GS for AIIMS or not can be understood only after going through a general comparison between the two:

Academics: The academics of both colleges are somewhat similar.

Lifestyle: KEM is located in Mumbai so you will have to go through the metro lifestyle which includes pollution, crowd, and an unhygienic lifestyle.

Hostel: Hostel facilities are much better in AIIMS than in KEM. Also, KEM does not provide hostel facilities to 1st-year students. The hostels in KEM are very crowded.

Crowd: KEM has a larger batch and there might be crowding.

The final decision is yours.