I have one of these fancy french baking books that says that the sourdough needs to be feed with a 2:1:3 ratio of water, starter and flour. But a lot of videos I see online basically just pour a little out, add equal parts of water and flour (seemingly regardless of how much starter they have) give it a mix and call it a day. What's the truth behind maintaining a sour? Not talking about storing in the fridge for now as the variation doesn't seem relevant to the question. Thanks for the advice!
Basically, at feeding time, remove half or more of your starter (otherwise the starter becomes too acidic, which interferes with fermentation), feed with equal parts by weight, flour and water. Maintain your starter this way until you are ready to build a levain for use in your bread recipe. Build your levain when your starter is at peak activity.
What it really needs is consistency. Whichever method you choose, make sure you stick with it. What you are doing is creating a colony of bacteria. You create a given environment, the microflora in it fights it out for some time, at the end one strain (or a handful of them) wins and takes over. If you change the conditions, another strain gets a chance and the war for ecological niches starts over.
As for what the exact "right" ratio and schedule is: there are many of them. This doesn't mean that any random combination will work - if you pull something out of thin air, you could get a colony of pathogens instead of good sourdough culture. Also, some methods might be easier to work with, producing more robust colonies, while others might be way to close to a bifurcation point.
So what you should do is follow a recipe. As always, there is a chance that you happen upon a bad recipe, or upon a recipe which is in principle good, but explained badly. You may prefer to use the more exact recipe from the book since the precision leaves less margin for error, or the more simple (but possibly less easy!) recipe from the videos, hoping that you will get it right despite the missing precision (or that it is so inherently robust that it never needed it in the first place). It is a personal preference for the method.
To make it even more complicated, you are also likely to end up with different taste profiles from different recipes. But you can't know for sure if and how they differ before having tried both. So unless you are in the mood for extensive experimentation, you cannot really use this as a criterion to which recipe you should pick. So you are back at just committing to one and see if it works for you.