I'm confused. Can anyone advise me BCA(computer application) is better or BBA(business administration). Why?

Well, I personally think that these two degrees are a LOT different; it just comes down to what area you want to pursue more. Here is some info on a BBA degree:

All business administration programs cover similar subjects within their core required courses.

BBA programs expose students to a variety of subjects: accounting, business law and ethics, economics, finance, management information systems, marketing, operations management, organizational behaviorand management,mathematics, statistics, and strategy.

The Bachelor of Business Administration programs allow students to specialize or concentrate in a particular academic area as follows:

Accounting
Entrepreneurship
Finance
Management
Management information system
Marketing
Operations management

Now here is some info on a BCA degree:

The basic objective of the programme is to open a channel of admission for computing courses for students, who have done the 10+2 and are interested in taking computing as a career. After acquiring the Bachelors Degree (BCA) at IGNOU, there is a further educational opportunity to go for an MCA at IGNOU or Masters programme at other Universities.

Basically these two degrees are different so I can't really say which is better so to say. Maybe someone can help you more on this but I would say that there ISN'T a better of the two just a different direction is career.