I write in large sketch pads, because I like the space to draw arrows and circles and make marginal notes. I used to write in Moleskin [sic] notebooks, but nowadays they just don’t seem large enough for novel-sized thinking. I save them for lecture notes, or lists, or personal journaling.
I’ve never tried to write a novel myself, but I have done some creative writing workshops, and I agree with Cat Rambo’s comment– larger size paper works better, in my case lined paper. This is totally in contrast to my adoration of pocket-sized notebooks with unlined paper. I use the small notebooks to make notes about things I might want to write, but the actual writing happens in a different format.