Having found both in a variety of circumstances, the shock of stumbling over someone (even when you are intentionally looking for them) can be disturbing in itself. Finding someone in the water is about the worst of the worst. Dismembered bits ARE disturbing but this depends, in part, on how recognizable they are. Curiously, Caucasian skin on dismembered bits is somewhat less disturbing (to me anyway) than darker skin as the contrast with darker skin is so stark and the flesh is easier to recognize for what it is. Although I search with dogs, some recent remains are stinky enough I can find them without the help of my K9 partner.
As surprising as it might seem, although a human skull is universally recognizable (pretty much across all cultures), they can be very startling to find in the woods out of normal human context. In real life, I have not met anyone whose first reaction to finding a human skull was “cool!” Perhaps that is because people who react that way are not often invited to participate by law enforcement. Even the forensic anthropologists rein in their enthusiasm on a real search. Maybe it’s because we know some of the history and life story of the decedent making the situation all too serious. Several weeks ago, we found a mandible and, because the teeth were still in place, it made it all the more human—various elements of dental work were obvious, etc. While we found other parts of the skeleton, the mandible generated the most emotion for me.
Speaking from experience, weather plays a HUGE role in how emotionally difficult different finds can be. A person dead several weeks in the winter is completely different from one dead a few days in the summer. Floaters are absolutely the worst due to bloating and consumption by aquatic critters (anthropophagy).
Aside from the skull, most people can’t tell human bones from animal bones, but the dogs, if trained properly, can make the identification just about every time. We proof them on roadkill and deer remains, so they know we only care about the human bones and they quickly “get it.”