Should an investor invest in a single stock A or Portfolio AB from a risk-return standpoint?

I calculated the coefficient of variation and wanted to double check if my calculation is correct? Do we divide standard deviation by return? When selecting the better investment, do we select the one with the lower coefficient of variation?

Stock A B AB BC Coefficient of variation = Average Return Standard Deviation SD / Average Return 13.43% 1.99% 0.15 11.57% 2.64% 0.23 12.50% 1.47% 0.12 11.14% 1.41% 0.13