Without being biased, (for ex. someone said the 1980 series is the best. I strongly disagree!) each version has its merits. I would start with the original 1960s version and then watch the other two in chronological order.
I don't know what this prejudice against the versions in English is or against dubbed versions vs. subtitled. I feel it is really personal preference. Remembering that "Astro Boy" is initially a children's program and should not be taken too seriously, I believe the 1960s original is the closest to Dr. Tezuka's ideals as it is the only version he worked on closely.
He was also very pleased with the American dub as he understood some of the necessary changes. It is true that some of the changes he did not like, but those specific changes had to do more with cultural differences and not with destroying his ideals.
Dr. Tezuka was personally dissatisfied with the 1980s version, (the original Japanese version, as he had nothing to do with the English dubbed versions) and he had absolutely nothing to do with the 2003-4 version as he had been dead for 14 years before its debut.
Of course if you really want to see Tezuka at his best and purest get one of the volumes of the manga. They have been translated into several different languages and you should be able to find them in a language you are capable of reading and understanding.
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