Temporary table vs pl\sql table

Hi , I've a process which need to do a lot of processing (summaries) on a large set of data.  

The main flow is as follow:  

   copy the new rows since last run (up to defined row count) to a temporary table.    Run various selects with group by on the temporary table and merge them into summary table.  

 I wander (I will conduct some tests ofcourse ) what type of temporary table will be better:   

1. create ... temporary table or ...
2. create type test is table of

The first option has more i/o and go throw the buffer cache , but doesn't consume a lot of memory the second option doesn't has I/O but consume more memory for the PGA.  

Any ideas ?      

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