I think they'll both be great cars. Each with their own purpose. The Fiat 500E is compact and great if your someone younger thats not married with kids, but if you are and need space, the Spark EV is perfect.
Power to weight ratio seems to come close on both, while the Spark EV is heavier, it has more power to make up for that.
Plus there's the styling and hipster side that the Fiat 500E has.
Really depends what your into and what exactly you need one of these for.