As already said, psych is heavy on memory, understanding concepts and then applying them- but mostly memory. With this, to do well you need to be working really hard throughout the year and ensuring you do lots of practice just like anything. I would actually think it is more work during the year, because it is heavy memory, but less difficult as such.
Chemistry is also a huge workload but in a different way. Arguably, it is less demanding throughout the year, as the content is less, but the understanding is a lot more complex. You need to be able to apply what you have learn in a number of forms, and be comfortable with maths and formulas. When you do sacs, you will be making mistakes and losing more marks due to error, or lack of grasping the concept fully.
Essentially it's about what you will enjoy doing the most.