Probably not what you're looking to hear, but there's no one 'best' detergent to use. There's sooo many brands out there and everyone has different needs, sets of circumstances and different preferances...
Honestly, my first advice would be to just keep things simple and stick with whatever you're using for your clothing. Unless it has chlorine bleach, bleach alternative or fabric softener built-in, then chances are it will probably be just fine. The cloth diaper internet world tends to confuse people in this choice because it makes it look like a complicated and difficult choice. The thing is, for the most part, all you'll see on forums like this one is people who are having problems and therefore have to really delve into detergent choice etc... You don't see the thousands of people out there just using whatever detergent they feel like and with no issues whatsoever.
I'd just say to make sure you don't use too much. No more than 1/4-1/2 of the 'recomended' amount. More than that is unnecessary and could build-up in your diapers and cause problems. Mainstream detergents nowadays are filled with tons of additives (like UV brighteners, stain releasers etc...) that are meant to stay in clothing even after rinsing. While this may result in brighter whites, it can also mean trouble for something like cloth diapers that are asked to perform in a way that your average t-shirt just isn't. You can stick to your regular detergent, just go easy on the quantity... This is especially true for you as you have a front loader, they can be particularly prone to causing build-up because they use so little water.
Soap nuts work wonderfully for many people, I personally love them! You could always add something like washing soda to boost cleaning ability (not that you need it, but it's harmless and might make you more comfortable -it's a major ingredient in mainstream detergents, plus it adds a little bit of a fresh scent that the nuts alone don't). You could also add essential oils for scent if you like your laundry to smell good.
If you really want to delve into the world of all the different detergent choices and wether they're good for cloth or not, then you can check out these links: