The 1tb fusion is pathetic and a disgrace.
It comes with a meager 24gb of SSD storage. 24gb. How sad, Apple!
It doesn't just end at insulting, and disgracing, their customers. Apple is disgracing themselves with a move like that!
It is a terrible idea to buy the 1tb fusion. Under no circumstances is it a good buy.
The 2tb fusion, when you unfuse it, is probably a better buy than the 256 SSD.
The 512 is optimal, and my personal recommendation.
If you need the storage, there is the 1tb flash option as well.
Just don't go with the 1tb fusion, it functions the same as a solo HDD.