If one want to go in the field of software development, what will be better for him B.Tech in CS or in IT ?

CS or EE or Computer Engineering. While I don't know your BS IT curriculum specifically (I've never heard of such a BS actually), generally IT pertains to helpdesk stuff, system administration, and buying and maintaining systems, not to software development and engineering in a primary sense. And when I've seen degree requirements in my industry, it is CS or EE (though they typically have a catchall). I have never heard of someone with an "IT" degree in my industry.

Look at the curriculum. Choose the one higher on math and with the more difficult and rigorous courses.

IT will be the best as there is a lot of scope of computers and softwares in the future.

CS

You already got your answers, but let me add this.

If you are from Andhra Pradesh, and studying JNTU, you might find both the branches literally the same. Everything from the syllabus(for three years) and the practical labs remain same. The only difference you find is in the final year of your graduation, where IT stresses more on the networking stuff. Also major part of the fourth year syllabus also is the same, but there is a variation only in the depth of the topics.
In short, IT was created only to increase the number of students studying in the collge(statement may or may not be entirely true).

Its cheap, best & easy option for computer science (IT) education

JSS International Institute of Professional Studies, JSS Technical Institutions campus, Mysore, India offers National Diploma (Computing) for 10th pass or equivalent and Higher national Diploma (Computing) for 12th pass or equivalent. These courses are certified by Edexcel, International, one of the main examination board of UK. After HND students can directly join for final year Bachelors degree course in computer science in UK, US , Australia or Singapore(conditions apply). Course duration ND 2 Years and HND 2 years. Method of assessment based on assignment, class test and projects.
for details visit http://iips.jssonline.org call 918212410255
Admissions are open