Process Id : Represents an unique Identification of each Process Instance. This number will be generated after the process invocation
Task Id: Represents each unique Task. One or more tasks can be created for each Long-Lived Process. Note that thi unmber will be generated even before a process is invoked. E.g If an user clicks on a process card from Start Process tab, a Task will be created with a unique Task Id. However, the associated Procedd Instance Id will 0 as the process is not yet invoked. Once the user fills the form and click Complete button, a Process Instance Id will be generated.
Job Id: Represents each job executed by the JobManager service. These Jobs are used internally and you usually don't access these jobs in your process.
So disregarding the Job Id, you may choose one from the two other options (Process Id or Task Id).
Comparison:
*One advantage of using ProcessId is, you can easily track the process details thgouh AdminUI. If you use Task Id, you will still able to track but need to find out the process Id first.
*The disadvantage is that the first user of the process cannot see the Process Id until the process is started/invoked. If you use Task Id, the first user of the workflow can see an Unique Id.
Hope that helps!
Nith
