I choose Arashi and Yamapi! Well, in fact, I don't really know the other bands (just by name). I saw SMAP in their vartiety show, but never heard their songs.
Yamapi : Even if I think he is a better actor than a singer, I enjoyed his album, and his las song (Ai Texas) is entertaining.
Arashi : I know them for less than six mounth, and I'm just beginning to listen to their music. But I like it very much. And they all are so cute (which has nothing to do with their music, though).