This are the most searched keywords ordered by the number of 3D models they already have (removing the half with most models, these can be viewed on the most amount of models page).
Here you can find unsaturated categories that are searched, good niches to start uploading models to. You want to look for keywords on the left bottom corner and the smallest bubble as they are the ones with the top position (left), more evergreen (bottom) and least amount of models (little bubble).