It depends, history is considered a facilitating subject and would be considered more favourable to universities but it wont matter to you anyway as you are already doing chemistry and biology which are also facilitating. I would check to see what topics you'll being doing in both subjects, I loved the AS History topics my school does, however I'm not as fussed about what we are doing now at A2, on the other hand with Government & Politics I didn't mind the AS topics but I really love what we are doing now at A2. So check the topics to see which subject fits with you're interests best. I would say that the type of exam you do for govt&politics is easier than the history one, but politics requires more outside research, as you need to use a lot of examples to relate to the question and this can really effect your final result, therefore if you want to do politics make sure you have genuine interest in it otherwise you'll hate your life for two years (though you can easily say this about any subject you do).