The person who was involved in the study of both Cuyabeno and Yasuní as part of the United Nations team at the time of the creation of protected areas in Ecuador in the 70's, along with the research team through an extensive study of both areas managed to determine that both are extremely rich in species, managing to remain as one of the areas that have not been surpassed by the number of plant species per hectare in an inventory conducted in Cuyabeno. Being ecologically equal, both Cuyabeno and Yasuní can be considered the most biodiverse areas in the world and therefore incalculably valuable for conservation.
However, there is a difference in the aquatic conditions since Yasuní has 2 lakes, while Cuyabeno has 14.
For people who like to observe animals from a jungle trail and from the water, when walking through the jungle wildlife is difficult to see high up in the treetops, so from the lower part of the rivers you can observe birds, flowers and mammals in the bushes and lower trees on the banks. Only from the water you can see birds, flowers and mammals in the bushes and lower trees on the banks, but this only works along narrow rivers and streams. On wide rivers, like the Napo, it is difficult to see wildlife, while the banks of the Napo were already almost totally deforested in the 70s.
Thus it is safe to say that Cuyabeno, with its countless rivers and narrow streams, is better for casual visitors and tourists. Likewise the Yasuní does not have such long waterways combined with lakes, nor its facilities operated by the Indians inside the park.
In the end, both areas are fantastic, and both need visits to politically justify the conservation of these large protected areas of rainforest (each with more than half a million hectares).