The pages are big enough to hold reasonable word counts, so you don't end up with too many pages, and it looks good sitting on pretty much any bookshelf. (*I only frequently see 6 x 9 Trade Paperbacks in SFF, so if you're not doing SFF, I'd steer clear of a trim size that large.)ĥ.25 x 8 is my personal favorite trim size. That'll give you a solid page count, and it'll look pretty standard sitting on a shelf. Given CS's rules on expanded distribution - which is limited to certain trim sizes - I would suggest 5.25 x 8 or 5 x 8, unless your book is especially long. I do have some running close to 5.5 by 8.5, but that's about as big as my thriller/crime paperbacks get.
Secondly, I can tell you straight up that 6 x 9 is not a common trim size in the thriller genre*, except in hardcover. Trade Paperbacks are meant to bigger and higher-quality than their tiny Mass Market counterparts, so when you're picking a trim size, you should base it NOT on what the Mass Markets in a genre typically look like but what the Trade Paperbacks in a genre typically look like.
Most of the paperbacks I personally own in the thriller/crime genres, like Michael Connelly and such, are Mass Markets, which is not really what CS offers. First thing you need to keep in mind - you're doing Trade Paperbacks, not Mass Markets.
