^It's not that simple, because not all CGI is alike. CGI can be great if it's got enough time and money and talent going into it; for instance, I found the virtual sets and scenery and creatures in Andrew Stanton's John Carter
to be pretty much flawless and stunning. But it's not at all easy to get CGI to look realistic, and if the time or money or talent isn't there, the results are not going to look as good as a well-done model shot. (And part of the reason JC's effects looked so good is that Stanton shot them as if they were live action, with restrained, physically believable camera moves, rather than the showy swooping about that makes so many CG shots look self-conscious and fake.)
In general, it's foolish to think a single technique is right for everything. The smart approach to visual effects is to make use of all the available tools in the kit, and pick the right tool for each job. There are still jobs for which miniatures work better than CGI -- which is why the CGI-laden Lord of the Rings
trilogy made extensive use of miniatures for cities like Minas Tirith (not to mention full-size physical sets for a lot of things that most productions would fake with miniatures or CG). One of the ways CGI can be misused is relying on it too exclusively, using it for shots that can be more effectively done with a different technique.