Each artist has their own preference for the right size, style, colour, fabric.
Over the years I've worked in everything from sewn books of handmade paper to the common black-cover sketchbooks. Every artist knows the black covers. The sort of industry "standard" with heavy cartridge paper inside and a black hardcover. I used to love the hardcovers. On my artist residency in Newfoundland I brought an A3 one and it was great to work in at the studio table. Ring bound sketchbooks have their place, to lie flat on a table for example.
Now I like to hold my sketchbook in one hand and sometimes fold the other side of the book over. So hardcover sits well on the shelf, but not in my hands.
My favourites are a range of leatherbound not-quite-A5 books. When I was working part time as a orders and packing minion for Immortal Longings - run by illustrator Elizabeth Schuch who started as my boss-lady but has now become a very good friend. (We've even done art installations together! Paintings for a corporate office and an installation for Essex Wildlife Trust.) Her small Shakespeare journals were just so nice to hold, with Italian ivory paper inside. When she was placing an order I decided to try a few journals with my drawings printed on the front. Just a small selection of about 8 images, one journal each.
They never really sold well. So I used them!
And was hooked. The size is perfect for my rucksack or a large pocket. It takes pencil, graphitone and even a bit of paint well. The cover is soft and supple and I can bend the sketchbook this way and that. It is chunky with 120 leaves so feels more substantial than a lot of the smaller commercial sketchbooks.
So now all my sketchbooks are special ordered. Since I don't need an image on them I can just order the plain leather. (Though I am tempted to do some Sharpie marker drawings on them!) Make in England by Whitehide so I feel I'm supporting a fellow small business.
Sometimes I consider ones with Shakespeare on them... especially Richard III. Because... skulls.