The RASC Observer's Handbook recommends a loose leaf 3-ring format. (See "The Observing Logbook" by Paul Markov, pg 86 in the 2021 edition.) The recommendation is based on being able to remove and scan pages into PDF format to share on forums such as this one. Some people here have mentioned using computer-based notetaking, including with tablets, phones, etc.
Ultimately it may not matter as long as you keep one. The discussions here on the subject were rather brief and sparse. Below are just a few out-takes, but I think that it about outlines the consensus here.
Star Dad wrote: ↑Thu Oct 17, 2019 3:43 pm I keep two separate logs -
1. An observational log of things I have seen with my eyes.
2. An astrophotography log that records object, what DVD images are permanently stored on, and whether I need to reshoot for more photons or because I need a barlow to enlarge the object.
Like others have said it's a personal preference. I use http://observation.sourceforge.net/en/ for visual recording and LibreOffice Calc (spreadsheet) for AP.
Max Nomad wrote: ↑Fri Oct 18, 2019 11:53 am Take the log book for example. When I bought my first couple of scopes and started learning how to use them I Googled like a madman, hoarding information and links like the Internet was going away next week. During that phase I downloaded a few logbook templates. Although these are spreadsheets and PDFs that would work flawlessly I ended up opting to use a journal program on a laptop. While the logbooks are great for things like observation contests I needed something a lot more flexible -- a blank text-friendly page to fill, something I could fill with both session data (e.g. - sky conditions, temperature, what I saw, etc.) along with my thoughts and impressions. Today I've got it set up to where I can use a diary app on my phone to grab quick notes on the spot, sync them in the cloud, then pull them up on the laptop and copy them over to the main journal.
The Astronomical League sells a bound notebook for keeping track of your work.
AL Visual Astronomical Observing Journal (Logbook) -- $16.00
The Astronomer's Journal is an 8.5x11 inch soft cover, spiral-bound, observer's log and sketch book. It includes 102 pages (51 double sided sheets) of logging pages which contains defined fields of entry (time, date, seeing, location, equipment, etc), two sketching circles, and room for the observer's own notes and additional information on the object. There are a few pages of a blank Table of Observations to be filled in listing the contents of the observer's recorded objects serving as a reference of the observational contents (a Table of Contents once completed), as well as a Catalog Information page to provide a brief description of the entire journal to keep it organized with your additional observing journals in your acquired set. It also contains an Introduction, a guide to astronomical observation journaling, tips for better observing, a brief summary of useful calculations related to journaling your observations, and a greek letter reference table.