It is more convenient for a horizontal sketch book to turn pages from left to right, just like many books, so it may be more convenient for people who are used to turning pages this way.
Vertical page-turning sketchbooks are more convenient to turn pages from top to bottom, which is the same as the traditional way of opening books in China, and may be more comfortable for people who are used to this page-turning method.
When choosing, you can decide which one is more suitable for you according to your personal page-turning habits and painting needs. At the same time, no matter which page turning method you choose, you should pay attention to the quality of sketch book and paper to ensure a good painting experience.