I personally wouldn't pick Durham, it's full of big-headed Oxbridge rejects! In London you have better connections and more opportunities especially for your field. There are some pros and cons for each. London is expensive, crowded..etc but tbh I would enjoy living in London as I see myself fitting there. If the two unis are equal academically, then I would encourage you to look into course structure, where you will be living, people that will be surrounding you..etc. It's not only about a degree, you will be living there for 3 years at least so go with your gut feeling.