Hello Saswat,
As both the courses are for graduation. So there is importance of each and every course at their own place. If we compare these two,so you should know that, The B.Sc (CS) course mainly focuses on the mathematical and theoretical foundations of computing, rather than teaching specific technologies that may quickly become outdated. The course prepares you for higher education.
other thing to consider when comparing BCA & B.Sc Computer Science is that BCA is more professionally oriented; it prepares you for post-graduate or research work and also creates professional manpower for problem solving through application of computer science at the interface of business and technology. BCA can also be pursued via distance learning.