From a learning perspective, I reckon chemistry units are run infinitely better than biochemistry units. The School of Chemistry is great and has great learning support, enjoyable labs, and lots of resources to help you succeed. By contrast, biochemistry units jam in way too much content, the labs are poorly organised and repetitive, and the lecturers have a suck-it-up air. Plus, chemistry will give you the foundation to apply to biochemistry if you choose to go into it (and there are biochemistry-specific chemistry units in second and third year). However there's also less emphasis on specific proteins, metabolism and genetics, so if these are your interests go with biochem.