Hi there,

1. IITS mumbai is better college than ism, but metallurgy as iit mumbai is not that good.
2. Ece is a better branch than metallurgy
3. Placements are better ar iit mumbai but metallurgy has an average placement.
4. Ece is going to be in demand in future.
5. For abroad iit mumbai is better.

Hence I would suggest go for ism... But if you want iit mumbai then you can change your branch after first year if your perform the best among your batch.

I hope this helps