I totally agree with My Mr Mermaid (the secondary couple was better than the main in my opinion)
Also seconding Age of Youth, all four girls have interesting stories and two (/three including AoY2) have romances and another has an implied future romance.
A Gentleman's Dignity has multiple couples, all of whom have different and interesting stories, as does One More Happy Ending.
Coffee Prince is pretty good for the main couple and the secondary
Shopping King Louie also has a cute secondary couple, and it a generally adorable drama
You're All Surrounded and Strongest Deliveryman have already been mentioned but they are great