I saw this on Behold Genealogy a few days as I was looking for something else – Comparing Raw Data from 5 DNA Testing Companies: http://www.beholdgenealogy.com/blog/?p=2700.
The companies tested were:
FamilyTree DNA (FTDNA)
If you go down a bit to the header: SNPs in common between companies, you will see how many SNPs each company has with the other companies. You can also find this information at ISOGG’s Wiki: https://isogg.org/wiki/Autosomal_SNP_comparison_chart. This is important because some companies share so few SNPs in common as to make them almost meaningless when comparing with other sites.