I would choose SOAS if you're concerned more about the course, I think it has an awesome reputation and specialises in global subjects like anthropology, but that's not to say you won't get a good degree from Sussex. Not everyone is suited to London universities so that's definitely something to bear in mind, I chose Sussex because it felt like it had a stronger community and I absolutely love Brighton as a place. If you get a chance, visit both and get a feel for them!