It’s easier for me to think in terms of “Comic Strips I Enjoy” than “Comic Strips That Are Funny”, really. Mutts, for example, is often not funny, but its warm, gentle tone is still a joy to read.
Arlo and Janis, though I suspect relating to this one is on the unwritten “You know you’ve been married too long when” list.
Barkeater Lake, for anyone who’s ever lived in a small town, or a city that still thinks it’s a small town, or…
Doonesbury - again, often not funny, but with a great cast of characters and a story line that almost always amuses, and often surprises.
For Better or for Worse - again, good characters, interesting story line, though the gags often fall flat
FoxTrot - Jason Fox grew up, I married him.
Frazz - intelligent humor on the comics page!
Get Fuzzy - reveals what Garfield could have been
Heart of the City - not always funny, but an intelligent strip about real kids. Also makes me miss SE Pennsy.
Lucky Cow - the Mon-Fri story line isn’t always strong, but the Saturday strips and the Sunday splash panels are worth the wait.
Non Sequitur - Obviousman can make my day
Pearls Before Swine - really good social commentary hiding behind poorly drawn animals
Zits - generally good at finding the humor both from the teenager’s point of view and the parents’, without being condescending to either, and that’s vanishingly rare.