I do both bio and chem, I think for psychology/neuroscience, biology would be better as we learn about the brain and neurones, etc, which A-level psychology students also learn so would be useful for psychology/neuroscience in uni. I think biology would also be better for environmental science as we learn about the nutrient cycles, plants, etc. At the end of the day, it's up to you, but as the above poster said, look at uni entry requirements of courses you're considering