There is a great deal to be said for giving to meta-charities like GiveWell or GWWC over directly giving to eg VillageReach: by sending an explicit message that you wish to give efficiently, it gives an incentive to charities to go for the efficiency dollar and it encourages others to give efficiently and to motivate efficient giving.

That said, I also believe that existential risk mitigation is a more efficient use of your donation.