Hi

Both the subjects are good and holds good future prospectives. I suggest if you have the option to take both go for it. It will double your chances for any future entrance exam. It totally depends on what do you want to do in future. If you want to go for engineering then you have to choose maths and if you want to go for medical or related career then go for biology.

If you take maths your future career prospectives will be statistician

Economist

Market researcher

Psychometrian

As for biology your future prospectives are:

Clinical ptoject manager

Biomedical engineer

Clinical project manager

Conservation scientists

So both the subjects hold bright future. Higher secondary maths is difficult and higher secondary biology is also is tough. Choose wisely. I prefer you should choose both as it will help in future and will make you eligible for both JEE and NEET

Hope this helps