The stock delco plugs are the best and the "hottest" you can run. You want those for a basic stock cars with maybe 1-2 add ons.

Its once you start dropping pulley does changing the plugs come into play. The goal is always to run the hottest spark you can, so thats when you go to a "colder" plug thats hottest for your application. Make sense? I might be explaining this wrong lol.