Does Size Matter?

What do you lean towards when buying books? Hardcover, paperback? Big, small? What's your pleasure? I'm curious! 

After recently going into Barnes and Noble, I noticed that most of the books are huge in comparison to mine. Perhaps I'm suffering from a bout of performance anxiety now, but I'm wondering what everyone's favorite sizes are. My thriller books specifically are small. They are 4x6 pocketbooks. I made them small on purpose because I've always liked the smaller books that will fit in a little bag and won't take me twelve years to read. Beach books, I call them. And while I did see some books of that size in the massive store, most were larger. 

My next book that's coming out is based in my hometown and has a special place in my heart. I'm considering making that one a hardcover, like the fancy books I saw lining the shelves of B&N. What do you think? Does it matter? Does cost matter? What do you look for when purchasing a book?