It would be interesting to hear Henry Allingham's view as to which he found more horrible. He's the 110 year-old veteran who's been on the TV today in relation to the 1st Veterans' Day commemoration in Britain. He fought at The 1st Battle of the Somme in 1916, and was on active service in WWII. An unscientific and unrepresenatative exercise, I know, but to ask him for his personal recollections and opinion would be illuminating from 1 soldier's perspective.
WWII probably involved far more non-military in the carnage. I'm thinking of the Holocaust and the purges by Stalin, for example, as well as those civilians killed in the Blitz and the firestorms of Cologne, Hamburg etc. And I wouldn't for a moment attempt to belittle the sufferings of the POWs in Japanese hands or, indeed, the soldiers on the Eastern Front. But I tend to agree with Loosehead in terms of the sheer horror and despair that must have confronted the Tommy, the Frenchman and, indeed, the Boche, in the trenches.