best piece of evidence?
well the discovery of Lucy, the australopethicus, is pretty convincing, it is a solid proof that we have ancient ancestors, and we evolved something else long ago, Lucy is the oldest KNOWN human ancestor. with the help of forensic science and other scientific fields, we are able to determine that species, esp. primates like Austrolopethicus, shared a lot of common features with modern H. sapiens, for instance, Austrolopethicus is believed to be the first species to walk upright on two legs
Darwin's theory of natural selection was pretty much strongly supported after his trip around the world on H.M.S. Beagle, he found adaptation in different kinds of species
Darwin got even more support when Crick and Watson discovered DNA, and proved that genes can be mutated and pass down to generations, and these mutations can be induced by the environment. and this difference in the genes helped evolution and natural selection (survival of the fittest)