I had pcmb with CS as additional.
I can say that both of these subjects are very heavy but to be more precise i I think biology is more of an advantage when you want to enter medical field or pharmacy also I believe. On the other hand computer science is very important when you want to be a part of software development or software administration. I can never think of comparing these two since it has no basis of comparison.
You can look up in details so that you know about your interests.
All the best.