Someone will correct me when I'm wrong, but here's my understanding:
OneStep is actually a cleaner similar to OxyClean, probably made out of the same stuff (sodium or calcium carbonate, probably). It's a cleanser, not really a sanitizer. Now, if you're starting with clean new equipment, then it might work fine to put your raw must or wort in there. But if you're using old plastic buckets with scratches and stains, then OneStep might not be a very good "sanitizer" for you -- it's really not a lethal chemical, just a cleaner.
Sulfite on the other hand serves as a sanitizer, but is probably not a very good cleaner. It kills the wimpiest of bacteria and wild yeast, but it also doesn't kill 100%, maybe only 95% or something like that, so you still shouldn't rely on a "quick rinse with sulfite water" as your main source of cleaning and sanitizing. However it should be an effective sanitizer when used with clean equipment. At least, it gets things "sanitary enough" for most fermentations, assuming that you'll be adding a lot of healthy yeast to your must or wort.
If you want the best of both worlds, something that can both clean and sanitize in one single step, and that doesn't even need to be rinsed, then I know of nothing better out there than StarSan. It does both. No need to rinse. Don't fear the foam. Don't use too much, a little goes a long way. Use as directed. This is what I use.
Iodophor and bleach also do the job very well and can both clean and sanitize. The problem with these is that they need to be rinsed, and in the case of iodophor, it also stains everything it touches. I used bleach for a while but it's smelly and doesn't taste good if you don't rinse all of it out. I never used iodophor and never will unless someone gave it to me free as it seems to be even more of a pain, but it should be every bit as effective as bleach.
That's about all I know about all the so-called sanitizers.