Hi I do AQA law (I know that's not OCR but yk) and have sat in Edexcel Politics lessons, I would say law is more interesting if you want to cover a broader range of topics, however it has a lot of memorising, whereas politics if you have a general understanding of politics it enhances it more and enhances the historical context of UK politics. So in general it's about what you would find more interesting, if your interested in both politics will be easier, however how parliament works will be taught in law. If you want me to give anymore information let me know!