don't know if this is a homework question, or a conceptual question, but I'm not sure there is a definitive answer.
It probably depends on the mutagen, as well as the specific cell type, and the amount of DNA, and the methylation, and the cell cycle, etc. Thinks likely balance out...like more DNA > greater oppurtunities for errors, but less DNA > greater impact of DNA change. Even within a Eukaryotic organism, mutagens may impact one cell type more than another.