I cross-shopped the Spark when I was looking at the Mirage in late 2014, and did some research on the Spark Forums. They were very depressing places, mostly filled with stories of various problems with the car, tales of surly dealership service managers, and corporate customer service problem-solvers who pretended to care but didn't. I don't remember much, but I do remember one thread title:
"Does anyone actually LIKE their Spark?"
It is my understanding that the 2013-2015 Sparks are much different in terms of problems/reliability than the 2016-up cars. I like the looks of either generation of Mirage more than I like the styling of the first-gen Spark, but I like the looks of the newer Spark better than either generation of the Mirage.
The Fit is a great car, but it is in another class. Prices on base model Fits start about where the price on a fully loaded Mirage tops out.