Hardcover. Both. First editions. Signed by the author. But I make exceptions for all attacks of whimsy. My most valued collectibles are books previously owned by my grandparents. I love the way they always signed their names into the inside front cover with the date and often the occasion. I would not trade these for anything including the collectible I most seriously covet - a first edition, signed of The World According to Garp. One day.
The lovely little chapbook of Praise Song for the Day by Elizabeth Alexander from Graywolf Press is starting to pop up everywhere. Was getting around to picking one up when my friend, Martin, showed up with one this morning - for me and signed. This surprise made my day for several reasons - I would have picked this up for myself in an instant given the opportunity, it was totally out of the blue, and I love presents. Many do not like to admit this. Instead, people say "Oh, don't get me anything," You don't need to bring anything," "I have everything I need," etc. If we ever get to know each other personally, and you hear me say any of these things, you may feel one hundred percent certain that I AM LYING TO YOU. Bring the gift. I will love your for it.
So I do not collect books for their monetary value but for their personal importance to me. They belonged to people special to me, they reached me at some memorable part of my life, the content was especially meaningful to me, or a really nice friend just showed up with it one ordinary morning. Such a sap.