It might be illuminating if you asked the dealerships which lobbied you to install either platinum or iridium plugs (at TWICE the already high $13ea normal cost for those plugs in most stores) whether they know why Honda did not use either platinum or iridium plugs as original equipment in 2006 Civic Hybrids; although they used them as OE parts in virtually all of the other models they made that year. If, as I expect; they don't know the answer, then this demonstrates why their advice should not be taken seriously. It also might be worthwhile asking them why, even if you were to follow their misguided advice, you should pay them $208 for the 8 incorrectly chosen plugs they want to put in your motor; when you could just walk down the street and save over $100 by buying a set of those same plugs at most auto parts stores.
As a career diagnostic and tune up specialist; during the last 40 years, I have repeatedly found that the original equipment plug brand in many engines occasionally does not work as well as some other aftermarket brand. The reason this is true is that spark plug manufacturers do not always specifically design or engineer a different spark plug for each new motor that comes out. They sometimes just specify a stock design that is already on their shelf. If that generic plug turns out to be a workable match, then it is OK; but sometimes a different plug manufacturer's generic plug for that application turns out to work better than the one made by the company that currently has the manufacturer's contract. Champion is well known for surpassing the performance of stock OE plugs supplied by other manufacturers. The classic example of this is the Chevy 4.3 liter V-6. This motor is known for its plugs breaking down long before their electrodes are worn to the usual replacement point.
My reputation as a problem solver escalated when I began replacing the original AC Delco plugs in 4.3 liter Chevy motors with the stock recommendation from Champion. In that particular motor, the Champions last much longer, give better fuel economy while doing so, and don't misfire like the AC's often do. It so happens that Champion plugs have a greater tolerance for combustion heat than most other plugs; and the Chevy 4.3 motor heats its plugs up more than most other motors do. There are about a dozen other similar situations for which I've discovered improved plug replacements. They are not all Champions; I use 5 different brands of plugs in the motors I tune; but I choose them based on how well the plug brand and model matches the motor I'm working on; rather than which plug manuifacturer now has the supply contract with the car company.
It makes me laugh to think of the times whan a car manufacturer has changed plug suppliers. What must this do to the people who always buy OE plug brands? Chrysler used Autolites in all their motors from WWII until the 1960's. But then they changed their plug supplier to Champion. Their motors were basically the same before and after the year this change took place; but those owners who were staunchly brand loyal must have had an ethical dillemma about whether to switch the plug brand they use. If the manufacturer switched plug suppliers in 1964 (I don't recall the actual year it happened) would this mean that 1963 Chryslers ran best on Autolites; while the same motor in 1964 Chryslers ran best on Champions? Or would it mean that the switch was done because Chrysler had found that as their engine design evolved and became more refined over the years; it became more common that Champions worked better in them than Autolites? But, if that was true; wouldn't Champions work better in the 1963s and maybe in the 1962s and possibly even the 1961s??? Or does it indicate that Chrysler lost touch with its time honored tradition and heritage; so the true believer should still use Autolites in ALL Chryslers; regardless of what the young radicals in the front office decide to do??
Then there are the American manufacturers who import Japanese vehicles and sell them as their own brand. The Chevy LUV and S-10 pickups were originally made by Isuzu. The Chevy Sprint economy car was made by Suzuki. Ford Courier pickups were made by Mazda. All of those vehicles originally came equipped with NGK plugs. But all the manufacturers who sold and serviced those vehicles used their own brand of plug as a replacement. WHO WAS RIGHT???
Please don't tell me that a Japanese car which came with NGK plugs in it will run better that way in Japan; but when it is imported and sold with another name on it; it will run better in the USA with AC Delco (if it's a GM vehicle) or Motorcraft (if it's a Ford), or Champion (if the vehicle is sold by Chrysler). That's just not so. Not even with OnStar monitoring.
Toyota owns Nippondenso Spark Plug Co; so their dealers sell ND plugs in the parts department. But some new Toyotas originally came with NGKs in them. The dealers sell NDs as the factory authorized replacement; but shouldn't the true owner use the ORIGINAL EQUIPMENT PART in those cars that came with the other brand? What happens if you buy a used Toyota? There is no way to find out which brand of plug originally came in it? Do you get the picture???
Sorry about the digression. To get back to the real world of 2006 Honda Civic Hybrids, there is an aftermarket plug brand called E3; which has thermal and electrical properties that offer potential advantages in performance, economy, and durability over conventional plugs in this particular motor. The E3 part number is E3.68. That would be my first choice in a plug for this motor. But if you prefer to follow tradition; I would use a Denso #4506 (PKH20TT). (That plug design was not available in 2006; but it is an improvement over older plug electrode technology.) If you REALLY want to follow exact tradition; I am not the person to seek out for advice. Instead, trust the experts at your local authorized Honda dealer.