I'm pursuing b tech computer science branch and i'm in third year which are the companies i should prefer for job?

The scope of Computer Science Engineer is great. IT sector is one sector which is not going to reach saturation. So far computerisation was in IT specific offices and organisations. But now computers are penetrating in almost every sector whether education, health care, travel& tourism, entertainment, automobile, banking and insurance, construction, engineering, telecommunication ... everywhere. So jobs for a computer science engineer will always be there in IT as well as in non-IT domains. Being a computer science engineer also gives the benefit of choosing any domain for career whether Networking or Databases or Software Development.

Hope this helps.