Wow, you guys, quite a thread; thank you for getting this conversation started Michael. The first example you showed had that visceral, gripping quality, that draws you in. Really nice. And desirable.
I played around with Advanced AO rendering in the beginning, like v16, until I discovered Brad's Softbox which I have used in Quality mode regularly for the bulk of my work ever since. I developed quite a library of luminaires, though, and did find that using the natural quadratic falloff gave me the kind of shadows I liked best. As much as I like to futz with the settings and tune the shadowforms, I've been focused elsewhere, so I appreciate the hours of test-wait-test you've all spent.
Michael, that final image is superb.
One other thing I noted, someone mentioned TCAD's rendering unreliability. If I do too many tests, sometimes the program stops applying my latest changes, and I have to save and restart the drawing; often I'll just restart the whole program to be cleaner.