In my experience, trying to choose what I care about does not work well, and has only resulted in increasing my own suffering.
Is the problem that thinking about the amount of suffering in the world makes you feel powerless to fix it? If so then you can probably make yourself feel better if you focus on what you can do to have some positive impact, even if it is small. If you think "donating to science" is the best way to have a positive impact on the future, than by all means do that, and think about how the research you are helping to fund will one day reduce the suffering that all future generations will have to endure.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.