There are so many dairy-free milk options out there, but it is hard to determine if some are actually more detrimental to the environment (almond milk, for example has a high sustainability rating on some levels, but I have heard the amount of water it takes to grow and harvest almonds is so high it might not actually be the best choice). Almond milk, soy milk, oat milk, macadamia nut milk, coconut milk- which is the most sustainable choice (and what do you need to look for in a label- i.e. Organic, fair trade, for which types of milk)?
There is one study that I stumbled upon recently. Of course I'm unable to verify this myself, but some trustworthy media like The Guardian and New York Times have articles citing it. According to these, it seems like Oat milk is the winner when it comes to the environment.
(Coincidentally it is my favorite and best to my taste)
Not sure if 'fair trade' is impacting the environment. I also don't know whether the organic harvest is more sustainable than the GMO as it is more complex subject and really depends case by case.
In my opinion, making your own milk at home must be more sustainable for the environment as we're cutting of the unnecessary transportation of water (which is heavy). If we already have access to clean water, it is probably the best for the environment to make our own milk out of grains/flakes.
For example, you can blend 1 cup of rolled oats along with 4 cups of water. You can look up for recipes online, but I still find commercial milks better and more consistent for specific use (like making cafe latte using oatly barista) :)
My personal preference, and the winner in this Guardian article, is Oat Milk. It has the best mouth feel, is easiest to cook with (imho), and as Sasho's response above and the article imply, is environmentally a great choice.
All the best!