Without Aguero, City do seem to be a bit wanting up front, having said that Barca are not the team of a few seasons ago, even so Barcelona over the two legs.
Arsenal... no chance! The Germans will win home and away... for too strong.
United have a chance against Olympiakos, away leg first always favored most teams, (not always) I don't think it'll be comfortable but United through.
With Dogbra going back to the bridge the 'Donkey' man will have to tolerate his fair play rule of diving, I think that's where Chelsea will fail at stopping him.
Barcelona
Bayern Munich
Man United
Galatasaray