That depends on a number of factors, such as whether the cursor is updatable, has an order by, etc.
It also depends on what additional logic would have to be implemented if a scrollable cursor was not used, but certain logic was required. But in general, a simple cursor is usually the same or more efficient if you don't need any of the features provided by a scrollable cursor.
You can check out the "Application Programming and SQL Guide" which can be downloaded in PDF format.
M. A. Feldman
IBM Certified DBA on DB2 for Linux, UNIX, and Windows
IBM Certified DBA on DB2 for z/OS and OS/390