will VS am going to VS am having VS will be having

will VS am going to VS
           am having VS will be having

I will have a party on Saturday.
I am going to have a party on Saturday.
I will be having a party on Saturday.
I am having a party on Saturday.
I am to have a party on Saturday.
I have a party on Saturday.

呢6句有咩分別呢?

By Kay
Reference:http://hk.knowledge.yahoo.com/question/question?qid=7008061302639