It solely depends upon you both are great colleges you will get great opportunities here both colleges have their alumni all over the world coming to choosing between iit bhu metallurgy and iit k chemistry the former is a btech course but the latter is a bsc course so it depends on you which course you want to pursue talking about placements since both are iits so you will get almost similar opportunity and it depends upon your hardwork to get handsomely paid pay packages leaving some companies many other would allow you to sit in their placement. Choose wisely!