Which group? Both!
Of the second group, the Koch Brothers are responsible - through corporate means - of plenty of deaths: to be fair, not in the same league as Stalin, though.
Of particular note are the many oil-related 'deaths' in Africa: you try and organize a union, or oppose Koch (or Koch-Glitsch), and a bad case of lead poisoning seems to occur with great regularity.
That's not mentioning the increase in deaths in the good ol' US or A, caused by lung problems ... attributable to fossil fuel emissions, and sustained gutting of EPA laws, and enforcement of those they can't get repealed.
Also wonder how many deaths can be attributed to the John Birch Society? Their father was a co-founder, and both brothers were members. A group that has had laid at its door, over the years, lynchings, preaching hatred (and the resulting violence), and funding of many other Patriotic, Anti-government, Anti-Immigrant groups (e.g. KKK, White Patriot).
Stalin was an abomination: Ché was a direct response to the de facto slavery situation in Cuba, including immunity to any criminal charges by 'The Masters', perpetuated by American capitalists run rampant; the Koch Brothers are a near-perfect example of American capitalists run rampant, merely with years of evolution of how to give themselves plausible deniability, and hordes of corporate lawyers to prevent anything ever being pinned on them.
Gotta love tricks like funding the anti-anti-XL-pipeline group, in Canada. Supplying transport and signs. And taking a page from another "By whatever means necessary" paragon, Roger Stone, regarding mounting protest signs being mounted on a solid piece of wood.
Oddly, most of the Koch funding of groups that support their goals use Structuring (a.k.a. Smurfing), which is a technique primarily used by larger criminal groups to hide where money is coming from and going to. Really, a corporate entity using the same strategy as criminal entities? You can draw your own conclusions about that.