Core branches are always demanding in nature so you will have to work hard in core branches. Coming to the comparison  you mentioned i would suggest you too go ahead with iit roorkee ece as ece is a branch that is related to it industry hence better placement scenarios are there whereas ee is a core branch and placements are not as great as ece comparing both the colleges iitkgp and iitr so there is nothing separating them they are both masters of their domain the only deciding factor maybe the branch in which iitr ece might win so choose wisely.