Difference depends on the usage. The related objects list on the bottom (relating object thru the interface) is really meant for general related objects through the XML fields.
If you have specific related objects you should use a datatype since this gives you more control.
This is very nice, but is there any way to know if an object is pointed to, from a relation that is stored in a datatype, as for the reverse related object list?
Actally, eor uses the same table than the standard object relation. You can use all the standard features to fetch related (and reverse related) objects.