Why is the nine tails afraid of Madara? In a recent episode of the Naruto anime, the reanimated Madara tries to summon the nine tails but fails since it's sealed inside Naruto, later when Madara attacks with his Deep Forest jutsu the nine tails tells Naruto,"I'd rather be controlled by you than by Madara" and shares some of its chakra with Naruto to defeat Madara. Is it really afraid of Madara or is there some other reason?
I don't think that it's fear per-se, more like... hate.

The nine-tails prefers to help Naruto voluntarily than be forcefully controlled by Madara (or Tobi, for that matter).

Manga Spoiler:


   The bijuu have feelings, and hate being treated as weapons, ever since the Sage of Six Paths dies, Kurama has known nothing but ignorance from humans. (Like when Madara yells at him to obey, or when Hashirama tells him that he's too dangerous and he must seal him.)  


So helping Naruto was the better option.