Call for Artists, Making Money at Juried Art Fairs, Craft Shows and Festivals
The answer is, it depends on the show. If your work is genuinely uncategorizable, mixed media is usually a good bet. It's a catch-all, and you'll be competing with some wildly varying artists. Glass would be a close second, even though you may use ceramic tile. Look at show web sites before applying and see if you can tell from the accepted artists which category will work the best, for that show.
Some shows will only have a few slots for the more unique categories such as 3D mixed media. 2D mixed media is popular with painters, collagists, some photography, drawing in some cases, and a host of other disciplines.
If you work is meant to hang on the wall, it's probably 2D, not 3D.