If you do not love Learning about all the other biology aspects (such as the structure of plants, biodiversity, etc.) I'd say go for Human biology, as in my opinion is far more interesting than just biology.
Biology is a very time consuming A level, on edexcel we do practicals and have to do a write-up of them, then there are question about these in the exams. The amount of revison prior to the exams varies on how much work you do throughout the year, but there is a lot of memorising to do.
If my school offered human biology though I would have taken that personally, but that depends on you. Of course every A-level course is time consuming, but expect to spend days and days to prepare to a good standard for the exams when taking biology.