[Senior Sherlock]

Any series I watch that is only 12episodes I will wish was 24. Any series I watch that was 25 I will wish was 50 and so on. It is tough to give my preference of episodes so to decide I will have to pick what anime produced that best episodes per amount of episodes available, which in this case makes it 11-15 episodes as my favorite length. If I like the anime no length will satisfy me, if the anime is adequate or worse then I don't really give my two cents on it.

PS: Clannad and Code Geass should be in the 50episodes, I don't know about most people but for me I don't believe a sequels following the same series belongs on it own.

[Twisted.]

I've loved both 12 and 25ish episodes...50 episodes is...good at times also.
The longer the series, the harder to sustain originality/entertainment imo.

[Ryan']

I can't even choose. I've seen two anime series's with less than 12 episodes, which I really enjoyed. Seen plenty of anime with the other anime lengths and I've enjoyed them all.

I don't really care what length the series is; as long as I enjoy it.

[sneekybasterd]

Only a few anime are still good over 24 episode mark, 26 at max, but there are those types of anime. Btw why no Eureka 7 on above around 50.😧