i have a friend who did both pe and chemistry, but dropped chemistry after y12 because she didnt enjoy it.
chemistry is definately harder, but i know that pe is not easy. theres lots you have to know for pe, a bit of biology chem physics history sociology applied to sports. i heard from my friend that its quite hard to get high marks in the coursework style work they have to and its hard to score highly in playing your chosen sports unless youre really good at it. which is good if you are!
chemistry is a smaller range to study. theres also no coursework. if you enjoy chem, you'll love the a level. theres no denying its hard work but the amount of work is smaller than most a levels