There are a lot of factors to weigh here... personally, I would rather fight in WW2 than WW1, mostly because trench warfare was a brutal, absolutely horrific experience, one fraught with constant disease and death, with a survival chance of next to nil. No good reason to fight, pointless and bleak, unlike WW2, which was fought for very obvious reasons and had a definite win condition. However, in terms of sheer human suffering, WW2 was a lot worse. The Axis powers did unspeakable things to the people they conquered, not to mention the scale of the destruction was much greater. The Soviets weren't much better, even though they at least didn't have a policy of racial extermination like the Nazis, the Red Army did practice ethnic cleansing on their way to Germany, and were immensely brutal to any Germans they found. Comparing some of the worst theatres of each war finds very little difference: both had their share of terrible conditions, though I would say that the Nazi concentration camps and the Japanese POW camps were much worse than anything found in WW1, bar none. Of course, before you got captured by the Nazis/Japanese you probably had a better chance of survival than a soldier lying in the trenches in WW1. Overall, WW1 was worse for soldiers, WW2 was worse for everyone else.