You have pretty much answered your own question. ArcExplorer will allow the user to add layers, web services, feature classes, alter symbology and run some minor analysis.
ArcReader is meant to be a reader for a specific map created in ArcGIS. The user of ArcReader can only view the contents of a published ArcMap .pmf. The user cannot alter the appearance of the data within a .pmf, they can only zoom, pan, identify features, and print a predefined map. You can create a map in ArcMap and then create an ArcReader package that contains the .pmf and all the data needed for the ArcReader .pmf.
We use ArcReader for our employees that work in the field and don't have an internet connection. We create a map package for them on a quarterly basis. It works well.
If you have ArcGIS Server and the Web Services with the data the user needs and the user has internet access then you would want to use ArcExplorer. You could also use ArcExplorer and ship the data in a file geodatabase (don't think .mdbs are compatible) to the user and then he could use ArcExplorer off-line to view the data.