I'm not exactly a yuri expert, but Doughnuts Under a Crescent Moon is my favorite yuri series that I've read so far. I love everything about it, from the artwork and character design to the setting to the emotional depth of the characters. It's a tender and relatable story about figuring out your sexuality as an adult, and all of the confusion and questions that entails. Bonus points for introducing a character who is one of the girls' ex/other girl's potential rival (kind of?), but not immediately launching the typical yuri jealousy-and-miscommunication plot.