Must see

Rating: 10/10 (23 January 2002)

If you're looking for sword fights, fantastic creatures, extreme violence or comedy, this Anime is not for you. If you are however, looking for an Anime with excellent music, a moving story, characters that you end up caring about minutes into the movie and animation that holds up well today... now you're talking. This Anime is for you.
In Grave of the Fireflies you are introduced to Seita and his younger sister Setsuko, two children struggling to survive in Japan during the heat of WWII. To avoid spoiling anything, I'll leave the summary at that. I will say this though, it's a somber story but one that any true fan of quality Anime shouldn't miss.
As for dub vs. subtitles, personally I found the dubbed voice or Seita to be just fine, while I preferred the original voice of Setsuko over the dubbed one. If I had to pick one over the other, I'd say I prefer to watch the Anime with the original Japanese voice acting with English subtitles. The strength of the original Setsuko voice being the deciding factor for me.
If you're looking for a moving Anime, look no further.