I would use pork: it's texture is somewhat similar to resembles human tissue. Some would use beef, but I wouldn't, if I were you. It holds less fat and a different structure, and can lead to differences in how maggots colonize and break it down. It won't align as closely with human decomposition scenarios.
Raw pork is the optimal choice for "maggots on meat" experiments in forensic entomology. Its composition, particularly the fat-to-muscle ratio, closely resembles human tissue, providing a reliable model for studying maggot development and decomposition processes under controlled conditions.