Periodically I'm asked, what is the best anime or manga for learning Japanese? I don't exactly keep up with every single anime series out there, and I suppose one answer is that the series that you like for their own sake are the best ones.
However, the problem with a lot of anime from the language learning point of view is that they are speaking colloquially. There's a lot of slang, improper sentences grammatically, not to mention the use of dialects and so on. A particular problem with some types of anime is the use of a kind of 'baby talk' which would be totally inappropriate for grown-up humans to use. With historical drama anime, there can be another problem - the use of archaic language that is never used in modern day conversation.
There's one anime series that stands out for me in just in terms of language use though: Fruits Basket. Taking its cue from the original manga series, the main characters and most of the side characters in Fruits Basket speaks in a very precise and courteous way - 丁寧 ていねい teinei. The dialect used is usually 共通語 きょうつうご kyoutsuugo, or 'common language', the version of Japanese that is mostly based on the dialects of the Kanto region that was standardized throughout Japan by the Ministry of Education. In particular, the main character Tohru Honda (本田透 ほんだ とおる honda tohru) speaks in a very polite way that would be considered ideal for a well brought up girl, which goes with her nature. You get to hear a lot of 敬語 (けいご keigo), or polite ways of saying things, from her.
Another advantage of Fruits Basket is that there are lots of long, storytelling dialogues with complete sentences (when they are explaining the Curse and all that). These can be better to learn from than chopped up conversational bits and pieces. The Fruits Basket dialogues are at a rather advanced level of Japanese, but it can be worth listening to.
Older anime series that were aimed at are good for learning in another way: they too use more 'correct', standardized Japanese most of the time.
Do you watch any anime series to learn Japanese? What do you recommend?