Which branch of B.Tech is the best? I qualified 12th and am preparing for B.Tech.

B.Tech in CSE or IT has more scope as compared to other specialization because these are evergreen fields. Although there is little slow down in IT field but it will never end up. You can also choose Mechanical and Civil. These are also good fields. Also, it depends on your interest and career goals

There are many branches in B.Tech field, but if you want you can opt for agriculture and food dairy department other than computer science and electrical Electronic Engineering.