The smaller size is just standard mass market size. It's pretty common for most books to have a mass market edition; at least, it used to be. The larger size you have is called a "trade paperback" edition, and is typically more expensive than a mass market, but less expensive than a hardback. The trades are often better quality than the mass markets (although, that's not always true).

Generally speaking, I prefer the mass market size, mainly because of the cheaper price; but that's also what I'm more accustomed to, as it used to be that many books would get a mass market edition, but not a lot of them would get a trade printing. Now, it seems, the trade editions are more common, and it's harder to find mass market editions. If you have any used bookstores in your area, though, I'm sure they'll be full of mass market paperbacks.

Sounds like a mass market paperback. They tend to be on the smaller size.

I love the book {When Books Went to War} and it talks about making books that could be easily sent overseas and read by Soldiers. Only tangentially related, but I think Vonnegut would appreciate it. Talked about which books were selected, how they were made and the emergence of some modern American classics that became popular through this method.

I don't know the measurements but I have quite a small copy of Cat's Cradle.

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