Here is something that will probably not change. My favorite manga of all time, thus far, is Fumi Yoshinaga's Antique Bakery. Why? Because, it is a storyteller's story. I like the mangaka's use of time. It's not easy to tell a story from so many perspectives, to timeshift the way she does, and she does it superbly. I like the characters, who are roughly my age (though they get younger as I get older:)). And I like their depth.
Additionally, this is a mystery. It doesn't run on for a kabillion volumes. It is nicely contained. It is dense and thoughtful, and it makes me hungry.