EDITOR'S OPINIONBillie Lou Watt- The late Billie was good, especially when compared to other actors in anime back in the 60's although she did have some moments that felt underwhelming (like the crying in her clip seems like it could have been polished a bit more. However, Billie does gave Astro a good sense of energy and personality so it's a good example of her acting skills.
Patricia Kugler Whitely: I'm sad to say that Patricia is probably the weakest one. Is she bad? Not really as her acting may have been a bit too monotone and it is a bit too obvious that Astro is voiced by a woman when compared to the other ladies in this compare. Still, while I've heard worst I would rank Patricia rather low.
Steven Bednarski: Steven has an advantage of not only being the same gender as Astro Boy but was probably the same age when he was first recorded as well plus had a very natural performance. He gives Astro Boy a caring and kind voice and I can easily see it fit Astro's other personalities.
Candi Milo: Candi isn't a stranger to voicing young boys but this is a nice change of pace for her. Candi was very convincing at making Astro sound like a young boy plus giving Astro an innocent yet playful feel but could easily go serious if the chips are down. This is an excellent example of Candi's and the show's voice work.
Freddie Highmore: Freddie is the same age (and gender) as Astro Boy and he does decently. While his acting could use some polishing his voice did fit well enough. The biggest problem I find is the movie did not do Astro Boy's personality justice, making him come off as generic and thus Freddie doesn't really have a memorable performance.
Overall my personal favorite is Candi but I thought Billie was a decently good second. I'd put Steven third, Freddie forth and Patricia as fifth.