See, Polytechnic in IT is a diploma course, while BCA is a degree programme course.

The basics lies here when you compare two courses.

If I talk about career opportunities, for a diploma holder pursuing degree programme further enhances one's opportunities for better job prospects like company,salary, profiles, growth opportunities in terms of advancement professionally as well as domain of your course of study.

It also depends a lot on your interest as well, if you're really interested towards field of engineering, you may pursue the diploma and further degree programme.

But, if BCA interests you, then go ahead with this.

In both the cases, higher study brings a lot more opportunities, in terms of growth career.

Also, make sure the college you're enrolling in, is reputed and provides good placement to candidates.