one of them引導的是並列分句。即分句＋one of them分句
這裏分句和one of them分句要用分號連接或者在one of them前面加連詞and/but等。
one of which引導的是定語從句。即主句＋one of which從句
這裏主句和one of which從句直接直接可以用逗號連接(非限制性定語從句),或者根本不用逗號(限制性定語從句)。
There are many books,and one of them is mine.
=There are many books; one of them is mine.（注意這裏是分號）
=There are many books, one of which is mine.