Actually, plats and multi-tip plugs are the worst for performance.
Platnium is a poor conductor of electricity. Silver is the best, followed by Copper, Gold and Aluminum. There are a few other metals before we get to platnium. Reason platnium plugs are used is because they are hard. They don't wear down as fast as copper plugs so you can leave them in the engine longer. The very first cars to come with plats were luxury cars. Why pay to change spark plugs at 20K, 40K and 60K miles when you can buy a car that needs them done once at 60K. Less maintainence was appealing to the non-car savvy elderly people buying those lincolns and caddys. Todays engines are so cramped, its a PITA to do plug changes. So that's why most car manufactures us plat plugs in almost all their cars. Now Platnium is expensive, so the plugs cost a little more to buy. And as we all know, sometmes people figure if it costs more, it must be better.
As for multi-prong plugs, well electricity can only use 1 prong at a time. It takes the path of least resistance. You could have 50 prongs and it will only hit 1 at a time. The other prongs just sheild the air/fuel mixture from the spark.
Mustangs are easy to do plugs on, so there really is no need for a plat plug. Changing them every 15-20K miles is no big deal. That's why you should just stick with simply single-strap copper plugs.
ytigyik 
