This isn't a category that feels WILDLY up in the air -- a few of the candidates seem well out of the race -- but it's also one where I wouldn't be shocked to see the de facto frontrunner upset.
Most people seem to be betting on Mad Max, and it certainly has strong credentials here -- the movie's imaginative visual design was one of its most praised elements, and the wild dystopian vehicles and stark landscapes make the movie's production design perhaps the most eye-catching in the race. But I think it's worth noting that the movie doesn't exactly have knockout sets. That didn't hurt Avatar -- the overall wow of the imagined world was enough to put it over the top. But I remember many betting on Life of Pi for much the same reason, and that lost to something more traditional.
That film was Lincoln, and I think if there's an upset, it's likely to be from the Spielberg film in this race as well. Like the film as a whole, the production design in Bridge of Spies isn't what you'd call innovative...but also like the film, it's pretty sturdy stuff. The movie covers a fairly wide range of locales, from 1950s New York to Cold War-era Berlin, and is handsomely designed throughout -- this category was once called art direction-set decoration, and this movie shows off the "set decoration" part of that title more than any of its competitors. It's also worth noting that more traditionally historical films have often triumphed over fantasy in this category, and even though Mad Max's ten nominations signal clear enthusiasm for the film, it's not as if Bridge of Spies's six mean nothing.
The Revenant seems like it would be a strange choice -- the backdrop for most of the film is Mother Nature, rather than any dazzling sets. And yet, the movie is quite popular with Oscar, it was pretty widely praised for the lived-in authenticity of its historical recreation, and Jack Fisk is something of an unrewarded legend. I guess I could see a scenario in which those elements propelled it to a win. But if Fisk couldn't win for the far more elaborate designs of There Will Be Blood, it seems like The Revenant will just be way too minimalist for this category in the end.
The Martian is certainly a handsome production, from the creation of the Mars landscape to the myriad of space shuttles and transport vehicles. But space-themed movies have tended to be also-rans in this category -- Interstellar, Gravity, and Apollo 13 all lost, and nothing in The Martian is so much more inventive it would stand out above those efforts.
I don't think anyone could seriously fault the period recreation of The Danish Girl -- it's a good-looking movie. But there's not much that's terribly imaginative about the design, and if The King's Speech (which I bet on that year) couldn't prevail with similarly textured interiors and Best Picture heat, I doubt The Danish Girl will have enough steam.
As in so many categories, I would probably have voted for Carol over any of the actual nominees, and I lament that, as with Far From Heaven, it was boxed out here. The movie is such a gorgeous and detailed recreation of time and place -- and a real time and place, not a Hollywood version of that, as in even some of these solid nominees -- I think it clearly merited inclusion.