Are you sure your school will allow you to do just two? We had to do all three.
Which will be easier is really down to your particular talents. I found Physics quite Maths-orientated, so if you're good at Maths, you might find Physics easier. Of the two, I found Chemistry the more interesting, and my interest in it generally helped me do better in Chemistry than either Biology or Physics. Does that help at all? My personal advice would be to go for whichever one you're most interested in...