Denso IK20TT spark plugs...

I didn't notice a big difference between platinum plugs and iridium twin tips. But hey the IR TT will last a long long time.

Don't know about platinum. I've used nothing but coppers in my 3 Spyders('03&'04 1zz's, '01 2zz) and my '91 Turbo MR2. My 2zz seems to run better...that is all...

 I remember long ago a friend of mine used platinum plugs on his old Ferrari that originally came with copper plugs from the factory and it didn't run right even after carburetor tuning. I let him know that platinum is a poor conductor and the reason they use them in modern cars is to extend the service life which is news to him because he believed like most people from the marketing that they ignite better. Once he switched to fresh set of coppers the car ran great without any misfires.  An old car like this probably didn't have the ignition strength modern cars have to overcome the poor conductivity of platinum. 

From my experience I felt that platinum and stock iridium plugs  were not as good compared to copper plugs for the Spyder but they just need to be gaped properly and changed out early otherwise the gaps open up and create a rough running engine the longer you use them.   A few years ago I decided to try the Denso twin tip that Galo used because I read about the literature of better spark kernel technology and I  actually felt that it  works better than the copper and will require less frequent change. I think they finally got it right with these plugs making copper and silver plugs obsolete.  

Yeah but it's a Ferrari. You give it American air and it won't run right. 

For what it's worth, I've used the cheapest NGK coppers I could find at a store, Denso iridium twin tips, and Denso platinums in my MR2. Back to back, doing some testing for something else. 0 difference. It's just a Corolla after all. For long term, I did keep the twin tips in.

@dev The conductivity of platinum or iridium may be poorer than copper, but it does not make any difference in a spark plug!  The distance along the electric path that is platinum is so small (like around 1 mm) that the total change in resistance is difficult to measure.  Put an ohm meter on the platinum pad and the center electrode near the ceramic and you will not measure anything.  Now compare this to the total resistance in a resistor plug or spark plug wires which is thousands of ohms and you will see what I mean.  

As I and others have pointed out, the thinner the electrodes are at the tips, the better the plug is for making a spark and letting the flame kernel develop, but this generally can't be expected to make a difference noticeable to the driver in almost all driving conditions.  This is because our engines run near stoichiometric to rich-best-power mixture all the time, with little internal EGR.  This is very easy to ignite.  So even the dumbest spark plug designs will work reasonably well in most modern engines.  The only conditions where our engines challenge ignitabity are during cold start (poor fuel-air mixing) and idle (high internal EGR), and near full-power (possibility of blowing out the spark due to high velocity and higher voltage requirement (Paschen's law)).  If our engines were calibrated to run lean mixtures, better plug designs would make a big difference.   

In the easy-to-ignite conditions, you could measure improved combustion stability (cycle-to-cycle) and possibility better 0-10% burn duration with a dual fine-wire plug, but it would be difficult to feel by driving the car.  The bottom line is the Toyota engines were calibrated with platinum or Iridium plugs and you will notice the longer plug life.