The best spark plug
 

I have a a 2002 Ford Focus ZX3 w/ 185k on it. What do you guys think is the best spark plug for it. Has anybody tried those max comp spark plugs?

...if you have FUEL ECONOMY in mind, a set of OEM iridium plugs gapped slightly wider than spec is preferred; but, if you're after POWER, a fresh set of "colder" copper-core plugs, gapped somewhat narrower than spec, is better.

I've had good luck with some Autolite double plats...will be trying E3s eventually.

I like Bosch spark plugs more than any other.

FWIW, E3's only seem to be "effective" in the older, carburetted engines, and "not so" much better in the newer, injected engines.

I prefer ngk platinums.

I've heard of racers gapping spark plugs narrower to eek out a few horsepower. But why would a wider spark plug gap increase fuel economy?

And wider gap would MAYBE decrease spark strength...but with a longer spark, you're likely to ignite the mixture more reliably...

I think power and economy go hand in hand...If you can make more power, your engine is running more efficiently, and more efficiently, we'll....

I run copper plugs in my SVT with a slightly bigger gap. Ford coils are good and strong and can handle the extra gap.
Copper is a better conductor than all those rare metals...but wears faster.
Iridium is designed for long plug life, and are not the best electrical conductor.

A wider gap igniting the mixture more reliably? That seems odd, a wider gap reduces arc intensity, and since the electric field is weaker as the plug gets old perhaps or something, the spark would not be as reliable.

wungun nailed the answers.

A wider gap increases the arc LENGTH (and thus AREA) within the A/F mixture between the electrodes, which provides better 'chance' of ignition of lean A/F mixtures which are often NOT easy to ignite--it's called increased "probability of ignition"--the difference in probability between a single-bullet and a shotgun-blast "hitting" the bullseye center of a target.

A narrower gap decreases the arc LENGTH in favor of a slightly HOTTER and LONGER arc duration, but assumes the A/F is always rich-enough to ignite easily.