The Giver or A Wrinkle in Time? (So glad no one's given me this one...)
A Wrinkle in Time, easily. The Giver is a good book, and I like it, but I don’t love Jonas the way I love Meg Murry (and Calvin and Charles Wallace, to lesser degrees). Anything to keep my girl Meg around!
Personally, I also feel like A Wrinkle in Time is a more unique and creative book - the basic conceit of The Giver is very creative, don’t get me wrong, but the story is still very similar to a bunch of other dystopias. Wrinkle, on the other hand, feels different from anything else I’ve ever read.
Lastly, if you factor the other books in both series into the equation, the other Time Quartet books are all quite good, while I think the Giver series became something of a mess after Gathering Blue.