I’ve managed to find a reference for radial engines; R-7 and R-9 radials, and therefore R-14 and R-18 radials, come out very well, better than the V-12 configurations in fact (ignoring the problems of articulation).

Interestingly the H-24 configuration, such as a Napier Sabre, comes out better than any V-12 too.

The W-12 configuration of the Napier Lion isn’t so good (again ignoring the problems of articulation).

However these are only theoretical measures of ‘smoothness’ for the main moving components and ignore any combustion effects.