According to the Guinness Book of World Records, the Bonobos are slightly more similar to humans, genetically, than Chimpanzees:
"Bonobos, primates similar to chimpanzees, which live only in the rainforests of central Democratic Republic of Congo, share 98.9% of their DNA with humans... Chimps share around 98.5% of DNA with humans."
This is contested by other sources (though it should be noted that the Book of World Records is fairly rigorous when documenting "records" and is very good about staying current).
It should be noted that disagreements on this point should be expected - according to the Smithsonian Institute, there can be measurable genetic differences between individual humans:
"While the genetic difference between individual humans today is minuscule – about 0.1%, on average – study of the same aspects of the chimpanzee genome indicates a difference of about 1.2%. The bonobo (Pan paniscus), which is the close cousin of chimpanzees (Pan troglodytes), differs from humans to the same degree."
Finally, it's important to keep in mind that, in the end, we're all far more similar than we are different. According to a publication by the Human Genome Project,
"a March 2000 study comparing the fruit fly genome with the human genome discovered that about 60 percent of genes are conserved between fly and human. Or, to put it simply, the two organisms appear to share a core set of genes."