Why is there so much disagreement?
There are so many factors determining whether a detergent is a good fit for you. Your washing machine, laundry routine, water type, and diaper choice determine whether a detergent will work well for you. There are infinite combinations of these factors, which means that everyone will have different levels of success with each detergent. What works great for one person might not work for someone else.
There are lots of other factors in detergent decisions other than how well it works too. Do your kids have sensitive skin? What is your budget? Do you want to use a chemical-free, natural detergent?
Is there one perfect detergent?
No! There isn't one magical detergent that satisfies everyone's requirements. If there was, there wouldn't be any argument.
Any detergent can be the perfect one for you. The only definite no-no (and I'm sure you can find sources that will argue this if you look hard enough) is not to use a detergent that has a fabric softener in it. It will cause buildup, and eventually repelling.
I disagree with sites that call some brands "garbage". Even detergents that don't work for some people may work really well for others. I don't think any should be written off. Some people say that natural detergents shouldn't be used because they don't get diapers clean enough. If your diapers are coming out of the wash smelling fresh, and you aren't getting any issues with smelly diapers or repelling issues, then they are getting clean.
How do I decide what works for me?
Try one. When you are deciding where to start, think of a couple of basic factors.
1) What detergent works well on my laundry now? If you have found that one works better than others (and it doesn't have fabric softeners), give it a try. Lots of common detergents (Tide, Gain, ALL) are popular with cloth diaper users.
2) Do you want to use a more natural detergent for your diapers? If you are concerned about chemicals or environmental factors, detergents like Nellie's may be a good place to start. It is made from more natural ingredients (which it lists on the bag). If you have a kid with sensitive skin, this may be a good option to try.
Start with a good, solid wash routine:
1) Rinse diapers in cold water (if you are using an HE machine, put it on a quick wash cycle to get out as much of the soiled matter out)
2) Hot wash cycle with long agitation and high spin. Use the recommended amount of detergent for heavily soiled.
3) Cold rinse.
How do I know if my diapers are clean enough?
Stick your head in the washer and sniff. Do they smell clean? If not, we might have to tweak your routine. If that doesn't work, it might be time to try a new detergent.
If your diapers are coming out clean, and you aren't having problems with bum rashes, unreasonably stinky diapers, or leaks, you are golden! Keep doing what you are doing.
Stains do not mean that your diapers aren't getting clean! Stains are just one of those things that happen when you have a kid pooping on stuff. They can usually easily be sunned out, and aren't a reflection of a bad wash routine.
What do I do if I am not sure?
Give me a shout. I am not militant about any particular detergent, but I can give you some guidance about some good ones to try, or help you adjust your laundry routine if need be.
Take all the advice you read in cloth diaper groups and forums with a grain of salt. Opinions can definitely give you an idea of where to start, but ultimately the right detergent for you will depend on what works for you.
Just remember, it is just detergent. Nothing is written in stone, and the world will not end if you try one that doesn't work for you. Just breathe, relax, and eat some chocolate while your diapers are washing.
Check out some great laundry products, that help with stains or skin sensitive detergents.