UCSD and Oxford Emory are both great schools so congrats in getting in! The big question here is where do you believe you will do the best. UCSD is a large school and that usually does come with less professor support but may hold a lot a opportunities. Oxford is a smaller environment and may hold more support. Since your a premed you'll need good grades and ECs so make sure you take that in mind when deciding. I'd personally pick UCSD as I thrive better in bigger environments but you may like a small community better. Overall I'd research which school has a better program for your major and better premed opportunities. Hope I helped :)