You can't go wrong with either. I'd favor the 4gb 480 over the 3gb 1060. I'd favor the 6gb 1060 over the 4gb 480. I wouldn't go with an 8gb 480 because I don't need an 8gb card and by the time I do I'm almost guaranteed to want something faster than a 480.
As to manufacturer, I just go with the ones I've had good experiences with. For me that means Asus, MSI, and EVGA primarily.