I go with the german one. katara‘s voice actress was changed after s2 which was a bit sad.

the characters sounded more mature and the character traits are better displayed through the voices than in the english dub, especially zuko, azula and toph. yes team avatar and co is young and yes ATLA is supposed to be a show for a young audience. I once watched it as a child (I was like 11) and I never looked back until I recently rewatched it as a young adult. I was surprised of how much ATLA is beyond a kids show. the show really freed me from the cliche that kid shows are only for kids. the themes it shows are targeted towards a older audience and they are quite political as well. Maybe Iam alone with the political argument. Iam not sure if a child can understand all those themes in it‘s completeness. my 11 year old me clearly didn’t but maybe other do. I don’t know. that‘s why I think that more mature voices do fit better for those characters. the only one who really had a younger voice was aang.

just my opinion, not a fact.