Whenever in doubt, always choose CSE over Metallurgy. Currently, CSE has a high demand. Back when a friend of mine was in his college, he mentioned how everyone went for MNIT blindly.
Back then, MNIT used to carry out classes of IIIT Kota. But currently, it is of no use! Even if you have to choose any college in the future, the streams Metallurgy and CS are likely to confuse you.
Just go for CS as Computer Science. As mentioned, it is in great demand and is better than Metallurgy. CS happens to secure your employment opportunities for the future. I also would not say that the placements are very bad if you go for MNIT, Metallurgy, the placements are fine, but not something that catches the eye, simultaneously. There is no tag of NIT here.