Hi Lesley, and welcome to cruise-chat.com.
The difference between the two categories is mainly location. The E cabins on A-deck are located amidships, whereas the EE are just forward or aft, but not all the way. Some of the EE cabins also have a sofabed, which will be a consideration if you are traveling with a third person. The E cabins still have sofas.
Note that there are also E cabins on Main Deck, yet these are further forward and aft. They also accommodate three or four pax.