Just as there is severity of turbulence, there seems to be a spectrum of quality too. Flying across eastern Oregon in the middle of a warm summer day is like riding a simmering sea of nacho cheese. The thermals letting off from the surface sort of bubble up, then descend back as they cool off, or surrounding air is displaced by warmer rising air. It's a mellower sort of turbulence, though I've been hit with thermals so hard that it couldn't really be considered mellow.
Mechanical turbulence caused by winds over terrain, or topographical features that impede the wind somehow, always seem to be much more sharp edged and violent, although ridge lift can be the smoothest and nicest sort of turbulence too. Got nailed by a rotor once in the Washoe valley coming off Slide Mountain that nearly knocked me out, swore I had broken a tooth. It hit so hard and fast that it was what I'd call of the harsh variety, whereas mountain wave, if far enough away from turbulence-inducing terrain, can be fairly "unharsh."
Then there are the shears. Faster moving air over/under slower moving air, where the differential occurs over a very short range of altitude. Those seem to be the sharpest edged, if we're talking mild. I've only been in moderate turbulence once, and that was more of the wave type in the mountains. Not so much hard bumps as it was a wild altitude rollercoaster ride alternating between full throttle, and no throttle.
Just recording some random thoughts on air quality as I stare out the window at the nice day and think of the Columbia river gorge winds.
My experience is not much and I'm curious to hear what others think, or have compiled in their experience as to the quality of turbulence. Some ____ are uglier than others.