In the long run I have no doubt that Greenpeace will have caused more damage than the Koch family. We could have clean energy right now if it weren’t for the decades of nuclear fear mongering, and the Koch family isn’t even opposed to nuclear.
Just in case this is somehow contestable, let me highlight a few points
* Climate change deniers oppose solutions that don't involve oil/gas/coal - this means nuclear power * Koch funding > greenpiece funding * greenpeice didn't start nuclear fear mongering, pro-oil lobbyists did - AKA climate change deniers.
https://www.greenpeace.org/usa/about/annual-reports-and-fina...
Their expenditures for all their "program services" (their various activism campaigns) was $27.4M in 2019 and $26.3M in 2018. If the Koch Bros. spend about $200M a year on activism, they're actually substantially outspending Greenpeace. Which, well, is to be expected: Greenpeace is a non-profit that's very often taking positions opposing major corporations.
(Greenpeace is actually a collection of quasi-independent groups around the world, but since the Koch's activism is primarily focused in the US, it makes sense to compare them to Greenpeace USA.)