If you are interested in one of them,go with it.Or if you have a confusion go with chemical.Because chemical is a rare course.Every years 1000s of engineers are coming out.so that  if you choose a rare course it will help you to have less competiton.

It entirely depends on you.
Figure the subjects which interest you.
Go to the site of the college you want to go and co pare the curriculum and the one you find interesting should be choosen.
If you have no specific interest and you are doing BTech only for a dwgree to have maximum Grade Point than in my sense go for Chemical because Machanical is abit tougher than Chemical, so maintaining a grade point is not that easy.

If you have interest in mechanical just go for it.