CoCROI based on free or total cashflow?

[Jónas Tryggvi Stefánsson]

When people (or you!) calculate the Cash on Cash Return On Investment (CoCROI) to  compare the profitability of a real estate investment and compare that to other investment options, should it be based on the free cashflow (income - expenses, not including mortgage payments) or the total cashflow (income - expenses, including mortgage payments)?

I thought that when referring to CoCROI one was not supposed to include the mortgage payment but I've seen people such as Brandon do it when comparing an investment to the stock market in one of his YouTube videos.

Thanks!