I read Huckleberry Finn decades ago, but I remember wanting to smack Tom when he cropped up at the end of it--and I had read Tom Sawyer several times. He's irritating even in his own book, but in Huck's he is insufferable. In part, I think--though, as I said, it's been years--because Huckleberry Finn is really quite a serious book, and Tom seemed incongruous.
I really liked Huck when I read it, but for some reason my strongest memory of it now is the part where he betrays his sex by snapping his legs together to catch something that is falling from a table, instead of spreading them wide to collect it in the skirt he's wearing as part of a disguise. I think I questioned the accuracy of the generalization, which certainly wasn't true at the time of my reading but may have been in the more skirt-wearing 1800s.