It’s kind of where your strengths lie. Biology is more if you know it, you know it, while physics is more application based. Also, biology is you take this general concept (like photosynthesis) and expand on it. Physics is you have this formula that is built on this other formula which is built on this other concept (basically, you HAVE to know and solidify your fundamentals, but if they’re strong, it isn’t that much more difficult that biology). You also have to consider what you can do with either (and remember you have ~2 years after high school to figure it out). Personally, I loved bio (which is why I’m going to be majoring in it next fall), but I also took physics and it wasn’t too bad.
Edit: Forgot to mention, physics is A LOT of math (especially calculus). Biology still has math obviously, but definitely a lot less and also a lot less advanced.