Hi Ahandoo,
I am not from your field but I can say that SOAS is University of London so you can go for it if you want that to be on your CV however, London is a expensive city when compared to Sussex and considering that IDS is also ranked high and reputed. So, it also depends on affordability and costs and overall ranking of the two are the almost the same. So, go with your gut feelings. Good Luck!
AJ