I don't think that question can be answered simply. Scale popularity (1/35, 1/32/ 1/30, 54mm) has varied over time and by theme (Naps, WW2, British Empire) as well as by manufacturer. From a WW2 perspective, 1/30 seems to be the most popular for WW2 figures in the last 3 or 4 years. Before that I think 1/35 and 1/32 were. Don't forget that 1/35 is one of the most popular modeling scales, although the 1/35 line of Minichamps armour didn't last long. And the Dragon 1/72 isn't doing as well as it did initially. The Corgi 1/50 scale did well for a while until Corgi stopped producing more armour in that series. The 1/32 line has also taken some hits with the closing of 21st Century and I am not sure where FOV stands today?
Terry