What is the most effective way to donate to AGI XRisk mitigation?

There are now many organizations in field of Existential Risk from Artificial General Intelligence. I wonder which can make the most effective use of small donations.

My priority is on mathematical or engineering research aimed at XRisk from superhuman AGI.

My donations go to MIRI, and for now it looks best to me, but I will appreciate thoughtful assessment.

Are there others?