Osamu Tezuka's original series
Astro Boy's influence on manga and anime cannot be understated. Osamu Tezuka's original series was a smash hit that set most of the standard tropes that would come to define traditional shonen stories, and it has received quite a few adaptations over the decades. The 1963 anime is mainly worth watching as a historical artifact, while the 2003 adaptation is likely to be most people's entry in the franchise if they decide to go with a series. However, overall, the 1980 version is the pick of the bunch, as long as realistic expectations are maintained regarding its animation (which is decent for the era).