I've been reading two really good 4-koma manga recently.
The first is Hitoribocchi no OO Seikatsu. It's about an extremely shy girl named Bocchi who made a vow that she would make friends with the entire class during her first year of middle school. The first person to speak with her, however, might actually be a scary delinquent.
It's so sweet and adorable that it's like a ray of sunshine. The picture in my signature is from this.
The other is Tomo-chan wa Onnanoko. Tomo is tall and strong and she's always been a tomboy. Because of that, her childhood friend Jun thinks of her as his buddy. Tomo, however, has a crush on Jun and she is ready to be more than just a friend but Jun seemingly has no clue that Tomo is even a girl. What really makes this hilarious is Tomo's friend. She's small and cute but with a bad personality--and she hates Jun. It can be hard to tell if she's trying to help Tomo or if she's just having fun watching them stumble around.