I'm just gonna come out and say it, I think Mob Psycho 100 has better writing than One-Punch Man.
They're both excellent of course, I was a fan of One-Punch Man before I read Mob Psycho 100 and I still am! But Mob Psycho has some truly amazing character development and drama, as well as incredibly multifaceted characters, whereas One-Punch Man has much more of a focus on action and comedy. Really surprised by how relatively unknown this series is compared to Ones other work.