For me it has to be 'Congo'
Watched it last night on Film 4. I was moved to tears. The narrative was just spot on. The cute and cuddly gorilla, authentic african scenery, the camps in real african jungles, the sad moments when the gorilla had to leave its human friend for its own kind and the part where the lead heroine lasers a tree to fall in the path of the male lead so he can escape a raging lava flow was so authentic it was believable. Why dont they make more films like that. When the credits rolled, the parents of the names on the film would be so proud of their children for creating this masterpeice.
The Mission impossible series come a close second in my opinion.