Trim size comes down to genre. Fiction and most nonfiction use Digest (5.5" x 8.5") or US Trade (6" x 9"). Children's books typically use Square, Small Square, or Landscape. Photography, art, and cookbooks print larger at US Letter, Portrait, or Large Square. BookBaby offers 12+ trim sizes total, viewable here. For paper, uncoated stock has a soft, traditional feel and is best for text-heavy books. Coated stock is heavier and slightly glossy, which makes color images pop, so it's the right choice for photo books, children's books, and comics.