Specific analysis of specific problems. Because these three subjects cross each other, which part do you want to see? And for different people, the difficulty of the three is different.
If you are good at calculation and mathematical thinking, of course, mathematics is easier. If it is a way of thinking that pays attention to models and experiments, it is naturally physics. If it focuses on the application itself, or innovation, of course, computers are suitable. Focus on the theoretical way of thinking, or find the corresponding content in the three.
Whether you are eager to learn depends on people.