Sir I got rank of 1900 in JEE Advance 2015.With this I am likely to get Chemical in few IITs and Electronics in IIT-G and IIT-BHU. Which one should be prefered first, IIT or the BRANCH.

Hi
This is completely dependent on your interest . if you are aware of the benifits of the branches and have genuine interest in that branch then go for the branch.

If you have deliberations over that , then you should go for IIT college. Moreover you get an oppurtunity to get a branch of your own choice if you perform well in your first year.