非限制性定语从句同时先行词被最高级修饰,用which还是that?

非限制性定语从句同时先行词被最高级修饰,用which还是that?

都有可能,看具体的使用语境。比如:

It is the most interesting book that I have ever seen.

It is the most interesting book, which I think you should read.