Hi Anuradha,
If you are into HR, decide upon the course based on your functional area. If you are currently a generalist with an interest in Compensation and Benefits management it would be good for you to learn SAP Payroll. However, if your interest is towards employee engagement and Org Development, go for the SAP HR course.
You'll have to think of your career progression path and then decide upon the course. Discuss with your Superior and get a feedback from him/her and then decide.
If you are student and want to become an SAP Consultant, decide the course based on your interest. If you want to be an HR professional, wait until you have some HR Functional knowledge before you do the course.
Regards,
Neeraj K. Singh