Depends on the producer, really. Cost is also some determination. As someone who used to work in the props/miniature department for Toho in Japan, miniatures can be tremendously expensive. It also depends on how it will be presented. Miniatures, such as building sets are often combined using CG to detail the miniatures further and to composite them with the rest of the image.

Most often today, it's not a matter of one or the other, but a combination of miniatures, CG and matte painting, as well as 3/4 builds that only go up, say for a building, one floor in the build and then use CG to extend them up the rest of the height of the building. It really depends on what it's going to be used for. There are just some things that miniatures can do that CG can't do effectively. As an example, the destruction of Venice in LEAGUE OF EXTRAORDINARY GENTLEMEN couldn't have been done well in CG. It would have looked too much like CG instead of realistic building collapses, though CG was certainly used to enhance it.

CG is wonderful, I love CG, but sometimes you just have to use actual physical objects to get the right look and physics.

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