How to copy table data into another table

Dear All,

I have a table t1 with 500 000 000 records in it and need to copy t1 into another table t2.

Kindly ask you to tell me which could be more efficient way to this task?

1. insert into t2 select * from t1;
2. use expdo/impdp (export t1 and then import it in t2 with append option)

does impdp work more fast than insert statement? or does it use the same techniques as insert statement does?

Thank you all.

Regards,

David