By 'objectively' do you mean something like:

"A subjective but widely/generally agreed Average Utilitarianism with high distribution of utility (e.g. low Gini Coefficient)"?

Water Aid immediately springs to my mind, but it is no longer recommended by GiveWell. https://www.givewell.org/international/health/water. Which highlights some of the problems with this objectivity and effort.

Perhaps malaria charities are the current 'best bang for buck' / best targeting 'a better world' with the fewest competing interests.