I have several of the Calvin and Hobbes books, and have been rereading them a bit recently.
I enjoyed one storyline which seems to have a number of twists. It starts off with Calvin ready to turn in his math homework, only for the numbers to leave the paper and the paper to catch on fire, then Ms. Wormwood turns into an alien, and then Calvin wakes up from his dream... Only to remember that he forgot to do his math homework that's due that day, so he and Hobbes get up to do the homework, but when observing the snow outside go back to bed hoping school would be canceled. Then school does become canceled, but instead of doing his homework Calvin plays in the snow all day (it's a wonder his parents didn't check to make sure he finished his homework). And then at school Calvin is worried about getting in trouble for not doing his homework, only for the closing bell to ring right before the teacher is about to collect papers, giving Calvin more time to do his homework. It looks like he's finally learned his lesson, only for him to once again procrastinate ("From now on, business before pleasure... And it'll be a pleasure to get that homework done."). And then the story ends there, with us never knowing if he did get the homework done in time.
And I like the storyline where Calvin accidently breaks his dads binocolars (by throwing it at himself to catch and missing). He spends his time being worried about his dad getting mad, and when he admits to his dad that he broke them, dad yells at him, with Calvin expressing that he already feels bad about it. Eventually the dad apologizes for how he behaved and admits it's not the worst thing he could do ("when you turn 18 you'll probably wreck the car...").
And I like the ones involving the box, such as when he uses it as a time machine to go to the future to pick up the homework he's supposed to do, and when he learns future Calvin didn't do the homework, they blame the Calvin from between when Calvin left and now. And then there's the time the box was used to turn Calvin into a tiger. But I feel the best ones are when he duplicates himself, learns that his dublicate is such a jerk, and becomes horrified when his dublicate makes more duplicates. Not to mention a later storyline where Calvin duplicates his good side, which begins with us not knowing what's going on. In the 10th anniversary book Bill Watterson explained that that's the kind of story that needs to wait until audiences are really familiar with the character.
As for some of my favorite single-story strips, I like the sunday strip where Calvin's mom let's him smoke a cigarrette, and after he does and has a coughing fit, his mom asks if he's learned anything, and what Calvin learns is, "trusting parents can be harmful to your health". And I like the Christmas strip where the dad jokingly acts as if they're just going to put the tree in the garage and not even decorate it. Not to mention a strip that's all pantomime, where Calvin goes to wait for the bus, realises he forgot his lunch, and goes in to get it, at the same time his mom sees the lunch and goes to the bus stop to hand it to Calvin. They eventually find each other, but then the bus leaves. After mom drives him to school and returns home, she sees that they forgot Calvins lunch, to which she screams.
In the 10th anniversary book Bill Watterson said that he thought it felt awkward for the short-lived Uncle Roy to not refer to Calvin's parents by name, which made him decide not to give the parents any regular contacts of their own. But in the strip where Calvin meets Uncle Roy, Roy refers to Calvin's dad as "bro". Wouldn't that be enough? And I wonder if this caused any problems when Rosylin babysat Calvin (Watterson could have at least given Calvin a last name so Rosylan could refer to the parents as Mr. or Mrs. whatever).