ignore the other answers.
the bottom line is a-levels are pretty stressful. the last thing you need is to regret picking a subject that you don't particularly enjoy for whatever reason.
go with your heart, whatever subject you enjoy more is the one you should pick. both subjects are very academic so the choice should be a little easier. if you like the subject you will perform better. doing an a-level you dislike is a terrible, draining experience.