I don't own either, but, I am in the same predicament you are and after my research and for my needs I decided I would get the fuel version.... have you actually held the two in your hands?
The fuel, for its slightly bigger build, doesn't feel much bigger, and is imho so much more useful.... the non fuel reportedly kills batteries in no time and has limited usefulness in a lot of aspects... where as the fuel is apparently a beast of a tool... ymmv but I think it's a no contest for the fuel one...
One thing to consider is Milwaukee is just now releasing the gen 2 m12 fuel drill and impacts. I would imagine those come first and then the hackzall would come next, so in the near future we may see a m12 fuel gen 2 hackzall that will give the size of the orig brushed model with the power and features of the fuel model... as that is the blueprint they followed for the gen 2 m12 fuel drill and impact...