I'm an old winemaker, so star-san and Iodophor are new(ish) to me. I always potassium metabisulfite for sanitizing, until I started making beer.
It works for sanitizing equipment. BUT- it takes a longer contact time, a pretty heavy concentration of sulfite (and it stinks and is irritating to the skin and lungs). I never use sulfite any more for sanitizing, not even sanitizing my wine equipment- I use star-san almost always but sometimes will use Iodophor.
There are a couple of advantages to these other sanitizers- one is the color and/or foam. You don't have to wonder if you've hit every spot- they coat the surface so that you can see what you've done. Star-san can be kept for months once mixed, so a gallon of mixed up star-san can last a long time.
One Step works, too. I used that in the past as well, and never had an infection. Any of these sanitizers are really personal preference. I like the handy markings to measure the star-san, and I like that it doesn't have any staining or odor. Others like some of the other sanitizers. Pick one, and see how you like the ease and convenience.
Broken Leg Brewery
Giving beer a leg to stand on since 2006