I make my own soy milk with soy beans and the soyajoy! Fresh soy milk is my favorite but I think you need to be someone raised on it or level 10 vegan because it is not sweet at all and is like delicious bean drink.
For me, it’s more of a question of what’s most sustainable. Afaik, soy is planted and harvested in Germany too, but oats are just dime a dozen around here, so I stick to those. Plus, I like the taste a little more compared to soy. Soy yoghurt is vastly superior to oat yoghurt, however. Coconut yoghurt is abysmal except for breakfast yoghurt with fruits and baking 💀
I never really just drink any plant milk, most of my consumption is as creamer in my coffee. For that purpose oat is superior at this point. Just get a barista blend and it stirs in perfectly.
And I completely avoid almond milk (in the US) mostly because it uses a huge amount of water and for whatever stupid reason we grow almonds in places that don’t get rain.
I am a soy supremacist but it’s hard to find unsweetened stuff. I have a sweet tooth but I prefer to keep that to deserts, not everything needs to taste like a lollie.