When I set up a long-term-project model for a contest, I make sure that it can be seen from as many angles as possible- usually on a platform made of clear acrylic, elevated by four 1" standoffs, above a mirror. Lately I have made use of a Scale Motorsports display stand. Not inexpensive, but worth every penny. I put my entry as close to the front of the table as possible, which is not always easy, and I'll have data sheets with the model- what it's based on, any added details, scratchbuilt or fabricated stuff, etc. If I don't want the judges to touch a particular model, I will indicate that on the registration form that accompanies the model. That usually works, but not on Staten Island. In those few instances where I have a hinged, moveable part, I'll be sure to change it's position as the contest progresses. Sometimes I'll bring a model that was never intended to be a contest model for various reasons; usually, I won't mind too much if a judge picks up one of them, especially if it's not displayed in an advantageous manner. I'm not saying that I like my models to be picked up but I understand the need to do so.
When I do judge, unless the builder has specified differently, I will pick up the model- especially if it is not displayed so that it can be seen. There are all kinds of things that can be hidden in plain sight on that chassis such as missing or loose components, missing paint (i.e., bare plastic), mold marks, tool marks and seams that don't belong there. On more than one occasion, I wanted to pick up a model for a better view- the visible stuff looked good enough to want to see the rest- only to find the body not secured to the chassis. Mind you, these were not funny cars or anything else with a lift-off body. If you're gonna use a stand, keep it basic and simple and make sure that as thew much of the model can be seen as possible. You don't want to detract from the model- the least amount of glitz and bling, the better. Too much might cause one to wonder if you're trying to camouflage something. A turntable is a good idea- as long as you can see the chassis- because the judges would be able to see just about the whole model. Get to the contest early so that your entry can be close to the front of the table- there's nothing worse (well, I exaggerate...) than having to crane and stretch to see what's wayyyyy in the back, especially when it's flat on the table with a "no touch" sign next to it.