Archive notice: This article was originally published on October 29, 2014. Links and embedded videos are preserved as part of the historical record.
Human models or other characters perform best, followed by scientific or medical models. Architectural exteriors and military objects are also popular. Another important finding is that models offered for free boost sales of the other objects by 60 percent. The optimum price category for high-class models is between 100 and 200 US dollars.

If you are interested, you can download the infographic here for a closer look.
And here you can go to the 3D model marketplace CGTrader.
Downloads: