> What are the pros and cons of running an ArcGIS Workforce application in Portal or AGOL ?
ArcGIS Workforce in general, functionally works the same in both ArcGIS Online and ArcGIS Enterprise. However, ArcGIS Online supports the more recent ArcGIS Workforce update (and works with ArcGIS Field Maps), while ArcGIS Enterprise does not (yet).
Perhaps you should consider this at a higher level, should you use ArcGIS Online vs ArcGIS Enterprise overall - unless you have access to both.
Hope this helps,