Fastest Insert

what will be the fastest way to insert 8000000 rows in a table

create partition table with all constraints and indexes then import

or
create partition table then insert into from other table then create constraints ,indexes.

Where are the rows now? Is it in a table or flat file or export dump?

in a table

Assume Table T1 has data, and you want to move to T2.
Here is what I will do:

Disable all indexes or drop.

alter table t2 nologging ;

alter session force parallel dml parallel 6;

alter session force parallel query parallel 6;

insert /*+ append */ into t2 NOLOGGING select * from t1;

commit;

alter table t2 logging;

Create/Rebuild all indexes.