If you have the opportunity to visit, I recommend Nagasaki over Hiroshima and especially these two places in Nagasaki:
Shiroyama Elementary School
Nagai Takashi Memorial Museum Nagasaki
These felt much more personal than anything I saw in Hiroshima and there were zero (other) tourists to interrupt the experience (very much unlike the museum in Hiroshima).
Shiroyama Elementary School
Nagai Takashi Memorial Museum Nagasaki
These felt much more personal than anything I saw in Hiroshima and there were zero (other) tourists to interrupt the experience (very much unlike the museum in Hiroshima).