Hi,
I haven't applied to either or experienced either course. However, I have applied to a course knowing that I wouldn't enjoy it before. My advice would be to research it a bit more using a direct approach: reaching out to current students.
SOAS seems nice as far as I can see, I have messaged someone using Unibuddy about Chinese there and they were very helpful. Maybe try that for the department you're going into as students tend to be more open about any shortcomings or nice aspects to their courses.
Another thing I would recommend is a little of reflection on your part with regards to what it is you want from your degree. Both the unis are generally well ranked in your chosen field, however King's does tend to pull ahead of SOAS. So I ask the time old question do rankings matter to you?
Wish I could have given you more substantial advice.