Pozzovivo definitely is a dark horse for the overall victory. He was in the shape of his live until his crash at the Giro. Also, he always starts a grand tour like fireworks before fading away in the last week. This time the Vuelta basically is over after 2 weeks. It depends on whether he can pull out a fantastic tt again.
Nibali won't ride. Aru and Landa are fresher and peaked for this. No space for Nibali imho.
Aru is the big favorite. This time he hasn't been ill and should carry his peak shape with him. Also the steep walls in Spain should favor him.
Landa has got to slave again. But I doubt he is gonna hold back this time if he climbs stronger than Aru again. Aru really has to earn his leadership this time.
Froome, Quintana, Valverde, Purito are all tired from the Tour. They won't be pack fodder if they go, but except maybe Quintana they should be too worse to take the win.
I got no clue about Majka to be honest. He should be a bit tired too, but seems to have a great recovery. That said even if he was fresh I don't know his level against the others. Giro 2014 seems years away in terms of his development.
Bardet just really got back in decent shape towards the end of the Tour. Maybe Ag2r can field both him and Pozzo here as dark horses and try to win the race. The steep walls normally should favor his explosivness as well.