BCA has more technical knowledge with the inclusion of programming languages like Java,C,DS,C++, Databases(MySQL, Oracle) etc. Thus one may get a decent job in a company even directly after getting BCA degree whereas BSc  CS (assuming you are asking for B.SC CS ) contains all the concepts, thesis and fundamentals of computer that one needs to know before entering into a computer field. Subjects like mathematics(boolean algebra, equation solving, graphs), microprocessor achitecture, history of computers and generations of computers etc are part of this course. But BSc won't provide the technical knowledge on any particular technology like Java, Oracle etc. They would just touch technological products like MSOffice and Java, but never in detail.

Note: Kindly consider your interest and potential before making any decision.

Hope this helps!!1