I've just finished chemistry a level and I absolutely loved it. I didn't take geography but I have loads of friends who did and really regretted, geography was the most taken as level in our sixth form but then around half of them dropped in second year because they found it very boring and basically all they were doing was memorising loads and loads of facts for the exams. IMO chemistry would be more useful in life as it helps you develop your analytical skills and general scientific knowledge, although i'm sure geography is also a very useful subject to take. You will be studying whichever subject you choose for two years so the main thing is make sure you can picture yourself still doing it and enjoying it in two years time.