Three Days of Happiness which is actually the light novel title. The manga adaptation title is "I sold my life for ten thousand yen per year" but I like the LN title more. I recommend reading the author's afterword in the LN if you finished the manga.
Kaguya-sama: Love is War. The manga itself is great but reading it live and discussing it on the old site elevated the experience even more. While I wasn't the biggest fan of the ending, everything else was just so good it's hard for me to give it anything but a 10.
I don't know that I can pick any one favorite, it's more like they come and go at different times. My current favorite is probably what I wrote about this week in the general thread, The Moon on a Rainy Night, but that is surely heavily influenced by recency bias.
A handful of other favorites of mine would be (tried hard to limit myself to 5):
Yotsuba&! is great! I wish it got more recognition is a hilarious manga rather than just a stepping stone for Japanese learners.
My favorite though is Kaguya-sama: Love is War. The characters are all insane in the most perfect ways. Skip and Loafer is a close runner-up though; I love its characters for all being so grounded they feel more like people than manga characters. It's a very different feel than I get from other manga.