Your choice of travel sketchbooks is personal. You need to decide on the size and type of paper you are comfortable working on. Then you need to adjust the size of the paper based on how fast you draw and paint.
Through trial and error I have discovered that a 5 1/2" x 3 1/2" Global Art Sketchbook works well for paintings I do in small spaces and quickly. For my paintings and journal entries I do in our travel studio (in Italy it is our dining room table in the villa), I use an 8" x 10" sketchbook filled with Arches 140 lb. Cold press paper and Raffine mixed media paper. I make this larger book myself and use rubber bands to hold the paper in place. These rubber bands replaced the binder rings I used to use and allow me to do double page spreads and give me the option to move the pages and bind everything later.
This trip to Italy was a busy one, so I made a lot of small sketches and only used a few pages in my larger book. Now that I am home I am beginning to work in the larger book using my photos as reference. The question is, do you touch up your unfinished paintings you did on the spot in Tuscany if they are a bit unfinished? Or do you leave them be as a spontaneous record of your trip? Tell me your opinion, please.