You have not mentioned anything about your interest. All fields are good and the returns are directly proportional to the handwork you do during your course with full dedication. It is possible only when you find it interesting.
So, my first suggestion will be to go with your choice. If we talk about job prospects, B.Sc. Agriculture is good field with lots of scopes in the area of research. Candidates ca pursue higher education and ca join agricultural firms, industries and even research institutes working towards improvement of agriculture technology. Teaching is again a good option for you.
In case of Biotechnology, as its name says, it is the field of Technology which is still in growing stage. You ca find many job options depending upon your qualification and these options are not limited to agricultural firms only. You can join Agricultural firm even wth your Biotechnology specialization.
Living & Learning- simultaneous processes!