I have used very thick notebooks, and I have use very think notebooks; everything between the Travelers Notebook refills to huge A4 notebooks with around 500 pages.
There are good and bad things about both and everything in between. These days I tend to prefer the ones in between; like the hard cover Leuchtturm1917 A5 notebooks. Because I think they are the perfect compromise between not taking a lot of space and being very heavy and being too expensive because you run through a lot of notebooks.
The good thing about smaller notebooks is that they are small, you can fit them almost everywhere and they are not very heavy. Perfect examples of this are pocket sized notebooks like Field Notes and both versions of the Travelers Notebook; I always go with the latter if I want a notebook but don’t have a lot of extra space. While the good thing about the huge notebooks is that you get a lot of notebook for your money because there are more pages to cover the cost of the cover, than if you have smaller ones.
What’s right for you? Well, it depends on you. I would try out different M-x postformats. And different formats will probably be good for different I use the smallest possible notebook (a Nock.co pocket sized one) for writing lists on the go, and I keep my journal in a Travelers Notebook because the think refills and soft cover makes it possible to always have it with me. But when it comes down to task management and drafts of larger texts I prefer Leuchtturm1917 A5 notebooks; enough pages that they last for a long time but small enough to not be a hassle to bring with me every single day.
I have come to this conclusion after trying out more or less every single format available over many years, and tried them out for different kinds of use cases.
The process of figuring out what works for you is something I personally think is very valuable, because it is the only way to find the best options for you. And I always try to identify when something isn’t working anymore.