For me, AH physics isn't that hard if you keep on top of the work. It's basically higher physics with a bit of higher maths (calculus for equations of motion) and a few other things like derivations of all the equations. The questions in the exam are also less 'guided' and of a harder standard than higher expectedly. If you're organised there is no reason why you can't do 3 investigations like you could do each of them in a month.
AH maths is different from higher. There is a change in emphasis from knowing methods and applying them to working things out from your understanding of maths. If you had no problem getting your head round higher maths, you should find AH maths manageable. If you struggled to understand concepts in higher maths you will find AH challenging.
Overall, I would say maths is harder content wise and physics is harder workload wise but a lot depends on your own personal strengths. Also, if you enjoy a subject it suddenly becomes a lot easier, so pick whichever you find most interesting if you're not sure about difficulty.
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