do you read those books?
which is the rarest?
I do not read the books. Part of that is because I have a two-year-old running around the house, but I'm not sure I'd trust myself even if I didn't. I have another wall in the same room covered with the same built-ins that house my reading material. Mostly hardcovers, a few Easton/Franklin bindings, but mostly run of the mill.
The rarest book would have to be the 1540 Synodi Nicenae. Beyond that, I'm not real sure, because I'm not looking for rarity per se, i.e. purely the number of copies that were published. I'm looking for sets that are certain editions, that are finely bound, and that survived ~150 years complete and in good condition. For example, there are plenty of Goldsmith sets out there, some of them more nicely-bound than mine, but I wanted a set that has hand-colored illustrations, and those are relatively hard to find. Bronte was the set that surprised me the most in how difficult it was to find.
The hardest to find was Bancroft's History of the US. I actually bought my set from a seller who, unbeknownst to me, was critically ill. She passed away before shipping the books, and her father contacted me to say he was cancelling the sale and refunding the money. I didn't have the heart to ask him to send the books, and spent the next year and a half looking for a replacement before the same set popped up and I snagged it. Most of my books are published and presumably bound in the UK, so my guess is that the set was of relatively little interest over there and to fine bookbinders. Plus, two of the books were published later on, so many of the sets that are out there are 8 volumes instead of the full 10.