Sorry for late reply. I am still not able to get a result. I guess this is because faculties of goldsmiths are striking in recent.
the answer is three main reasons as me.
Firstly, RCA and Saic are more expensive tuition fee than goldsmiths. Espacially for international student. I felt it is truly unfair!
Secondly, there are many artists in goldsmiths who I have admired. They actively participates in current international art field such as biennale and international film festival and so on. I believe that goldsmiths has the best staff and tutors among these schools.
Lastly, I like curriculum in goldsmiths that fully focus on not only art practice but also research about current huge amount of contemporary theories such as in socio-political, geopolitical and technological perspective.