A Level Philosophy or History? Watch
History is facilitating, therefore technically would be considered the most 'respectable' in theory, given that it is one of those desirable foundational subjects. I haven't found it too difficult, and the jump for me personally was non existant. However, getting an A* at GCSE doesn't ensure immediate success so you may find it difficult. I think history is very subjective, many people find the content relatively understandable but take time to adapt to the new question styles which are definitely much harder than GCSE. However, if you're a committed student the workload will not be too intense providing you keep on top of notes and revise for things, handing all essays in on time. Overall history is a very enjoyable a level.
However, despite philosophy being non facilitating this isn't to say it isn't respected or hard. In fact, AQA philosophy (the pure course) has been named one of the hardest a levels, and I can atest to that as it is very challenging. The content you are exploring is alike nothing you will have studied before, and the questions really make you think. There is a reason why the pure philosophy exams are 3hours long for a disproportionate amount of marks - it really makes you think. The debate skills and writing skills you get from philosophy are incomparable to any other subject and will adequately prepare you for law.
I would actually urge you to consider taking both, as if the humanities are your passion and law is your degree route they will be incredibly complimentary. Just be sure to check that the philosophy course is the pure AQA one, with epistemology, mind, ethics and philosophy of religion otherwise you're essentially doing RE/P&R which is not the same thing and although is not a soft subject by any means is nowhere near as challenging.
If it's Philosophy & Ethics, I believe that's slightly easier than history.