I went to a big art supplies store in Shinjuku (Tokyo) called Sekaidō (世界堂) to check the different kind of sketchbook they are selling. They have a very large corner for watercolor drawing books. I didn't know which one to chose do so I just picked up one randomly.
At first I thought it was difficult to draw on it because the paper is not smooth compared to the paper we use in animation production but I got used to it. The good thing is that the sheets of paper don't wrinkle when you paint because they are thick enough. The watercolor doesn't dry too fast either, which allows nice gradation effects. you don't have to rush too much is you want to mix colors on the paper.
Although I'm satisfied with this sketchbook I'll probably buy another type next time to see the difference. I may prefer it or not, but the only way to find out it is using it.
Hope it helps!