Underwear, with the doctor lowering them at the precise time. Which for me, would be the highlight of the experience. Under the part where i enjoy undressing others, and being undressed BY others.
Nude wouldn't be natural for me. And i would think it would distract focus. The whole time, you might wonder if there's any focus on any or all of your exposed regions. With the dramatic drop of the drawers, the moment picks up with intensity as with the act comes an implied focus.
Whether you enjoy this as a stage actor or exhibitionist, there's a dramatic moment when the curtain is drawn, revealing something, and in doing so, creating a rush. The curtain in this case, the undergarment.
And of course choice of underwear: a jockstrap. Which is actually a cross between underwear as boxer/briefs and nude in terms of exposure. And being exposed in a jockstrap has a more dramatic effect, because there's extra revelation compared to underwear which basically provides the same amount of cover as shorts or swimming trunks.
Likewise if I were to watch a woman being examined, I'd prefer to see her start in a bra. Creating a dramatic moment when that bra is stripped off at the moment it is time to focus on the breasts being examined. The best kind of woman to watch being examined is one that is not used to having her breasts exposed to others and touched by others, and therefore seeming more awkward, a little more timid/shy, and having mild feelings of vulnerability.
Ever see the movie Being John Malkovich ? Well, this post is like a step inside the portal of the brain of my little head. As i re-read over this post, I can see it clearly deserves a writing credit.