LotR is definitely among the best, but I'll only count that as one. I read them when I was in like 3rd grade, but even when I didn't fully understand them, they still seemed to amaze me.
And the rest of the list, good or bad, will be assigned school readings, since I'm not an avid reader haha.
A Tree Grows in Brooklyn and The Giver were two of the best books I've read. The former is a really powerful, emotional story, probably the most mind-penetrating book I'd read up to that point. The Giver just had an interesting plot, which made me excited to read further, which doesn't happen often.
The worst books I've read are all classics that I don't really believe deserve the accreditation. Walden, Catcher in the Rye, and Heart of Darkness. These were all very long reads with relatively slow plot progression. They make up with that in powerful interpretation, but for me, I like to read books for the stories and hopefully get as much out of the meaning as I can. I don't care to try to squeeze out the meanings behind rather dry texts.