In my opinion (for what it matters) as long as the plug you get has the same reach as the stock one, it'll work.
there really is no benefit to spending big $$ on iridiam, or any other exotic tipped plug.
these are not high performance race engines, so any plug that will get spark into the cylinder will work.
of corse, an iridium plug will last a lot longer, but i can't justify spending that kind of money on a spark plug for a $100.00 engine.
you will not get any performance gain with an iridium plug.
you will however get a little performance gain by going from the stock china plug to an ngk plug. a better spark plug wire and boot will also help.