As third world countries, both Uganda and Rwanda are special and safe countries for gorilla trekking. There are several families in each country or game park and they are cautously protected from poachers. In Uganda you will also have the opportunity to see other primates and environments, including the tree climbing lions.
In Rwanda, you may be fortunate enough to be in a group led by one of Dian Fossey's guides who speaks to the animals as if he were part of their family. I'm not sure that he isn't. They love him so much. This adventure is a once in a lifetime experience. While expensive, the encounter is priceless.