Strongest Deliveryman! I'm sort of always hyping this drama because I really enjoyed it. The main characters are really refreshing, the female lead is tough and cold (at first) and the male lead is good and kind, to the point that he has loyal friends everywhere he's been. The story is, in a way, about the value of living as a good person. It's a very cute drama with a lot of great characters.
I also love Age of Youth to the point that I think everyone should watch it. It's extremely good. I honestly can't put into words how great it is, so just trust me on this one and keep watching.
Jealousy Incarnate, Reply 1997, and My Mr. Mermaid are also favorites, as is Strong Woman Do Bong Soon. I've rewatched all of these at least once.