Dittos again to the above comments.

Note that I was not implying that render quality was the only important variable, nor that my own commonly used solution was the ideal one. My comment was aimed, in a very general way, at addressing what I see often enough as a too common fault with a number of otherwise good pieces, both here and elsewhere - The artist is frustrated, or perhaps not - which is another topic altogether -  that his piece "doesn't look real enough." There may be any number of reasons for that, many of which have been discussed above in other posts,  but often enough the most striking fault, even at a quick glance, and aside from any other problems that  may exist, is the poor quality of the render itself. When it's suggested that perhaps a better quality render might improve the situation, it would seem that all too often the artist is unwilling to wait for the results of a high quality render. To this my question then is, "Then why even bother in the first place?"

This was certainly a discussion I've had with a friend of mine, quite artistically skilled and creative, non-digitally. He purchased Vue 4, based on some of my older work which he found interesting, and seemed rather angry and frustrated at the generally crappy results of his own efforts. The problems were many - including that his own creativity did not seem to translate well to this medium, but the primary thing was his own impatience. Hours spent on composing a piece meant nothing to him, but if the render could not be achieved in five minutes, well, he was done with it. Unsatisfied, of course, but done nonetheless. Oh well.

As far as the render quality used, I doubt that there is any single answer. It depends on what's needed, and it's hard to beat simple experience for that, but it's best to aim high.

Aspect ratio is interesting: I generally use a 4:3-ish ratio, not because it's "best," or anything else. (Quite the contrary)  My pre-digital background was in 35mm film photography, and I guess at some level, my attempts at photorealism kind of reflect this sort of ratio. Unless a particular subject absolutely, physically  demanded it, even heavily cropped stuff ended up with roughly this format. Damnable cement-headed rigidity! LOL

"La meta es el olvido. Yo he llegado antes."
Jorge Luis Borges,Un Poeta Menor,Oro De Los Tigres