Before I founded RegalBeagle.biz and The Bucko Soap Scum and Grime Cleaner, I worked at a small company that made laundry detergent for big box stores. One time, I was tasked to test a few store brands of laundry detergent with a some standard stains. I don't remember exactly which ones, but they were something like wine, grass, chocolate, mustard, and maybe oil.
I took some standard fabric, put the stains on, and ran the test with 3-4 brands of detergent and did one without detergent as a base.
All the detergent brands performed pretty similarly. All the stains mostly came out, and all of them struggled with mustard. Which is pretty normal.
But then I checked the load where I didn't use any laundry detergent... and it ALSO was mostly clean! (Except for mustard of course). So that day I learned, just water and the mechanical action of the washer basically takes care of most of the big stains.
I still use detergent in my laundry, I'm guessing because a part of me doesn't quite believe that result. But now I only use a little bit, unless the load is extra dirty, and I only use the good stuff.
What's the good stuff? I recently found an article from Yahoo and Consumer Reports that did an extensive test on name brand detergents. The winner won't surprise you, but Costco fans will love the runner up.