I think that at the margin at the moment, a dollar to One Step for Animals does the most to reduce suffering. Long-term, I think the work of The Good Food Institute has the biggest potential to reduce suffering.
My personal non-animal donations have gone to small organizations doing important work without a lot of recognition:
Transgender Law Center
The Trevor Project
Southern Arizona Gender Alliance
Obviously, though, small organizations can't undo massive structural setbacks. So I've recently donated to the senate campaigns in Iowa and North Carolina, with the hope being those dollars have the greatest marginal impact. No, I don't think my contributions are likely to make a difference, or that the expected value is the same as the amount given. But I think the ... slight hope? ... the donations provide me make them worth it, in the same way text banking, letter writing, and (previously) knocking doors did.