They’re both a considerable step-up from GCSE and what is considered easier will be subjective. I wouldn’t worry too much about the overlap between biology and the other sciences because it’s not that significant from my memory.
I would say pick the one you enjoy the most and feel like you can perform the best on. However, for physics in particular, a lot of sixth forms and colleges recommend you take a-level maths if you intend to do physics. Physics will have a significant amount of maths content and doing a-level maths will help you with the maths content within physics.
Additionally, if you intend to pursue physics later on, maths will almost definitely also be required.
So if you are not doing maths a level, it may be a better option to pick chemistry in my opinion.