Here are pictures of members of the top-5 genera: Pongo, Pan, Ateles, Gorilla, Presbytis (see Figure 2 in the paper)
Deaner, R. O., van Schaik, C. P. and Johnson, V. (2006) Do some taxa have better domain-general cognition than others? A meta-analysis of nonhuman primate studies. Evolutionary Psychology, 4:149-196. (pdf)
Although much recent attention has focused on identifying domain-specific taxonomic differences in cognition, little effort has been directed towards investigating whether domain-general differences also exist. We therefore conducted a meta-analysis of published nonhuman primate cognition studies, testing the prediction that some taxa outperform others across a range of testing situations. First, within each of nine experimental paradigms with interspecific variation, we grouped studies by their procedures and the characteristics of their study subjects. Then, using Bayesian latent variable methods, we tested whether taxonomic differences consistently held within or across paradigms. No genus performed especially well within particular paradigms, but genera differed significantly in overall performance. In addition, there was evidence of variation at higher taxonomic levels; most notably, great apes significantly outperformed other lineages. These results cannot be readily explained by perceptual biases or any other contextual confound and instead suggest that primate taxa differ in some kind of domain-general ability.
If taxa do indeed differ in domain-general cognitive abilities, then this could help explain the distribution of spontaneously occurring complex behavior. Thus, in primates, the great apes, the best performers across the cognitive paradigms, show relatively high rates of deception, highly complex manipulation, population-wide tool use in the wild, and robust mirror self-recognition (Byrne & Whiten, 1992; Tomasello & Call, 1997; van Schaik et al., 1999; de Veer & van den Bos, 1999; Inoue-Nakamura, 1997). By contrast, prosimians, which had the overall lowest scores, exhibit little manual dexterity and no tool use, deception, or mirror self-recognition (ibid). Future studies will be necessary to determine the robustness of these taxonomic differences and to test if the global variables also explain variation within great apes, monkeys, and prosimians.