Thanks for your replies guys, much appreciated and very interesting.
The results, also based on related discussions outside this thread, at the Luxrender forum, MoI 3D forum and on Facebook:
Most people think A is rendered with Cycles and B is rendered with LuxRender.
With regard to preference, the opinions are evenly divided. Some prefer the subtlety of rendering A, while others prefer the more pronounced reflections of rendering B.
Here’s the answer:
A is rendered using Luxrender,
B is rendered using Cycles.
For the Luxrender rendering I used the Carpaint material with a red / black diffuse shade and the three standard grey specular shades. I tried to mimick that as closely as possible with a Cycles shader containing three glossy layers with differing roughness, on top of a diffuse shader, and a Fresnel input for realistically converging reflectivity.
The other settings were also matched as closely as possible, including light strengths and DOF.
I used the exact same colors for the materials and the lights. The Luxrender rendering turned out quite saturated. I even slightly desaturated the reds of the Luxrender rendering in Photoshop. Cycles rendered the same colors with visibly less saturation, which helps establishing an impression of realism. I expected it to be the other way round: more saturation from a renderer using the limited RGB color range.
To get matching highlights I increased the Fresnel value of the Cycles shader, hence the slightly more pronounced reflections in that rendering.
As for my personal preference, I really can’t decide which one I like more, especially because I know that decreasing the Fresnel a little in the Cycles rendering would yield less pronounced reflections.
Please do not regard this little experiment as an instigator for another ‘my renderer is better than yours’ discussion. I just wanted to see if a non-complex rendering setup would already show differences in realism between a ‘physical’ spectral wavelength renderer (Luxrender) and a ‘non-physical’ RGB color renderer (Cycles).
All the best,