Well in my opnion unless u get powerful cpus like the ryzen or i7s , cpu mining will be more of a hastle then profit even with free electricity, unless u have a large bunch of them already like 30 or more . Even then to ROI the motherboards , the hdds ,the rams is gonna be very difficult , and even managing them and making sure they are cool enough is gonna be taxing , its better to do an acutal job .
I am currently mining electrenum with my ryzen 1700x in my mining rigs
But yeah if u go with cpu mining u should also look at storj or other hdd mining to increase ur already really low profit