That depends on what type of programming you are currently doing.
If you have a need to develop mainframe applications that use CICS, JCL or IMS technologies and would like to emulate this technologies on your desktop then you should look at the Enterprise Developer product.
If you are developing distributed COBOL applications without the mainframe technologies that will run directly under Windows then you should look at the Visual COBOL product.
Enterprise Developer is actually Visual COBOL with the addition of the mainframe technologies.