I want to paint my plastic grille and paint some metal trim , whats the best type of spray paint to use for both the plastic grille and the metal trim

This depends on the car. From your screen name I figure that it is for a Duster?
Krylon Dull Aluminum is a nice match, and it covers well. Totally Auto used to market textured Argent in both light and dark tones. These are certainly more expensive that the Krylon from the local parts store, but if you want a more factory correct appearance, they are worth a try.

I used wheel argent silver from Eastwood
HTH
Bob

Rustolium makes an argent finish product that is like the dark really wheel centers. I did a Mazda truck grill with it and it came out AMAZING. Flows super well. The cans spray tip put out a nice, broad pattern too.

I have to second the Rustoleum comment. I used their "textured plastic" rattle can paint on my Duster sharktooth grill and it looks great. I used the Nickel color which is similar to Light Argent.