All LoZ have been E10+ or Teen. Most of the Modern LoZ have been Teen which leads me to believe SS is no different. It could never be EC because EC cannot have any form of violence. M has never been in a LoZ game and I hope it will never be. Adult only should never happen, there are so little games that are adult only any way and I doubt SS is one of them. As for E I think that's a little too tame for a LoZ game. My guess is T.
Like everyone else here, I'm going to say E10 or T. I am leaning toward T now, because I have a feeling it's going to be a little more heavy and deep for a Zelda game. Even though this is just speculation, Ghirahim's words are very violent and such, and I don't know about you, but his tongue licking terrifies me. I think if SS has some mature values it might earn a T rating, but Nintendo might have been very careful and wanted it to be a E10 rating. I highly doubt that it's going to have an E rating, that doesn't seem right, and as others have said, Spirit Tracks had a E10 rating. M and AO are completely out of the question, as with EC.
I am sure it will be a T for animated blood. In the new Comic-con trailer when link stabs the skulltula blood definitely sprays out. They made TP a Teen because Ganon bleeds as he runs around so I believe that this game too will be a Teen for the same reason.
I think the rating system for games is rather flawed, but it will most likely be rated T. Zelda needs to be at middle ground between children and mature gamers. Under no circumstances do I think it should ever be rated eC or AO. Zelda needs to cater to all gamers.
I think E10+. I know this is different from everyone else's speculations, but just look at what Dragon Quest IX was rated E10+ for (Alcohol Reference, Animated Blood, Comic Mischief, Fantasy Violence, Mild Language, and Mild Suggestive Themes). If the ESRB is lenient enough... E10+.