I did art, English lit and psychology for my a-levels and loved all of them. I know a few friends who regretted choosing sociology over psychology as it involved far more statistics and human geography than they were expecting. Psychology is far more focused on individual experiences, such as why we conform to social influence, how the human brain can remember certain things and not others, and whether we truly have free will or not. I studied the AQA spec and found it did really well to include the multiple approaches to psychology throughout the course, from the biological approach (everything we do is determined by our genes and physical brain structure) to humanistic psychology (although we are influenced by biological and environmental factors, we ultimately have free will and this is the healthiest way for a person to think). A large part of the spec is also the 'evaluation' (2/3 of what you write in 'essay' questions) in which you strengths and limitations of each argument (i.e. the biological approach can be useful to forensics as it means that we can explain why offenders commit crime and we may even be able to predict crime before it happens. However, this implies that offenders do not need to be held accountable as this is purely taking a deterministic approach). This means that in the course you are not simply just learning facts but how to debate and compare as well.
In terms of which is easier to learn in a year, I think both are similar, so choose the one which interests you the most because that will be far easier for you to learn. There are loads of online resources for psychology, I would recommend psych boost YouTube videos, Physics and Maths Tutor (both for past papers and they have a huge PDF of revision notes which was a lifesaver multiple times) and Study Rocket. I think psychology is regarded the slightly more scientific out of the two so may appear more academic, but at the end of the day, it matters more which you'll enjoy and do better in, both are really good subjects.