Supposed to replace the washer with every oil change right?

Well I didn't for a few times and the plastic one that is there is showing a bit of wear. So I asked the local auto parts store guy for a washer for it and he asked me "plastic, rubber or aluminimum?" I wasn't sure... the plastic one wasn't holding up too well so I asked for the aluminimum one.

What do ya'll use and recommend?