I had find many had slightly confused with Agloanema species which is closely related with particular species. As for one, I would consider if it is Agloanema - there will be more red coloration on its foliage and colors included on the stem too.
Dieffenbachia however is very much grows tall and leggy, also bigger and hardy in comparison to Agloanema. Also factor is that the base dominant color is green with (white to cream tones) the difference of splashes, streaks and dots that makes the unique difference in the patterns which is somehow difficult to put in a uniform factor as each foliage is uniquely different from each other.
One thing that I seek to identify and class them according to my understanding:
The colors - some are just 2 tones and some are more than 3 tones.
I for one find that those are in 2 colored tone catagories seemed to be very stable in their appearance and also hardy.
The ones that have the shaded appearance like fades and watercolored paint wash - seemed to be more sensitive and may easily damaged and does succumb to rot.
The other factor is the hybridization and it's variety.
Technically speaking (or what I had discovered is that) Dieffenbachia seguine and Dieffenbachia maculata have similar characteristics and often crossed breed until they are most likely are of the same species.
D. maculata have unique characteristics where the leaves are more oblong shaped, sharply pointed and have fragile features in comparison to D.seguine which may be hardy and cane like.
However the D.amoena may too fall into the D.seguine category.
Here are the list Dieffenbachia (Dumbcane)
Do click on their names to get to the link to get into more detailed information
on each plant types and their characteristics.
Dieffenbachia 'Mayan Jade'