Request Type MPR: Which requestor to use?

I decided to try an experiment with a workflow to set the value of an attribute based on some criteria that can change throughout the lifecycle of the user account. I am trying not to use a set and a set transition MPR, so I went with the request MPR option. Unfortunately, I am now a bit confused on how to set up the requestor. Should I select the "Specific Set of Requestors" option? And if so, would I select Synchronization engine as the requestor? The target resource will be a specific set of users, and I am using a MIMWAL activity.