Real sets with enhancsments, all the way. With all this cg crap, they have gotten good at "seamlessly" comping the actors in, for the most part. What they sorely fail at now, and is just as bad if not worse than garbage mattes, is the difference in sharpness, contrast, and lighting between the actors that were comped in, and the environment that they're supposed to inhabit. That's awfully done. It always looks like they're standing in front of a movie screen.

The worst example of bad compositing in ROTS is with C-3PO on the veranda of Padme's apartment when Anakin leaves for Mustafar. Look at the difference in color, calrity, and sharpness between 3PO and Padme. It's insanely bad, especially the shot from behind 3PO looking at Padme when she says "No thank you, 3PO".