Maybe "one or all" doesn't quite hit the nail on the head. It's more like several shades of "many" that keep some readers happy. Basically there are two kinds of readers - those who will read one book at a time, and those who'll juggle several at once. Obviously the latter won't read with one book in the left hand, one in their right, and an eReader on their lap (then again, you never know), but they don't just settle for only reading one book all the way through before starting the next one.
I for one have never been able to make myself read more than one book at a given time. I start it and I finish it without any other bookish interruptions. Unless you count my time at Uni when I did plow through several books at once for my courses I never wanted to dip into several book worlds at once. So maybe there is a difference between reading fiction and non fiction when it comes to that, but these days it doesn't matter what genre, I'm a one-book-reader.
I've seen more than once how some folks have up to five books on their currently-reading shelf on Goodreads and, needless to say, I often wonder what's wrong with a certain book that you don't want to read it all the way through in one go? Alright, maybe you need to squeeze in a particular book for review, thus keeping another book on hold for a few days, but five books? That's ridiculous! Don't these people want to know what happens next? How the book will end? Or are those books so awesome they don't want them to end? Or worse, are they so horrible they simply can't continue reading? Who knows?
Maybe I've reached the age where skipping from one book to the other after each chapter will get things muddled up in my brain or, much more likely, this is just my bookish attitude - to live in only one book world at a time. The only reason for me to put a book away before finishing it is ... wait for it ... because I don't see myself finishing it. Ever. Say hello to my DNF pile! The thing is that I know the book is not for me and that I'll never touch it again, so why act as if I'd pick it up anytime soon?
To me it seems that if you feel the need to take a break from a certain book then there's something obviously not working for you regarding the book. It can be small things or big things. Small as in not being in the mood for it (these things happen, but then you shouldn't have started reading it in the first place; instead you could have waited all the way through November for your inner bookworm to feast on it), or big things as in banging your head against a wall and the urge to jump off a cliff if forced to continue (in which case you should declare it a DNF and go on living a happy life without any broken limbs and lots of other amazing books making up for the pain this one book has caused you).
As much as I eat every course aka read every book after the other some people evidently prefer to read buffet-style. Well, to each their own, I guess! How about you? One-book-reader? Or do you prefer your reading buffet-style?