How do we quantify how many people died because of communism or capitalism?

[Statilius the Epicurean]

I've said elsewhere recently that I think many critics of communism (and I suppose capitalism too for the purposes of this thread) focus too much on the shocking death tolls from man-made tragedies like the Great Leap Forward and not enough on the general failure to improve the standards of living of billions of people over the longue duree.

If Stalin had killed zero people then the Soviet model would still have been significantly worse than its competitors!