Bio technology has a very bright future if you are in no.1 position among your peers and also you need to have a very good knowledge of biological names

Computer Science as you can see is growing at a very fast pace and opportunities will increase after few years but you need to do other courses also along with your degree to get a good package

Mechanical is also a very good branch to take in case if you are good with the latest technologies implemented

All the best

It seems to me that you are unable to decide, which stream to choose.
Nonetheless, if you are looking for studying abroad then opt for Bio- tech, which is a growing field and will involve every other field in coming years.Don't choose this if you plan to study in India.

Opt for CSE, if you want a good placement after graduation.
Mechanical is good but placements aren't good until done from a A or B level college.

There you go.
All the best.