The first drama that comes to mind when you hear about recommending a drama to someone.

 ColourMePurple:

Does it have to be 1 drama? How about 1 from various genres?

Psychological: Girl From Nowhere

Action: Taxi Driver

Law/Military: Military Prosecutor Doberman

Thriller: My Name

Supernatural/Thriller: Sell Your Haunted House 

Horror: Hellbound

RomCom: A Business Proposal and 18 Again if they don't mind a fantasy element

Fantasy: Hotel Del Luna

Medical/Comedy: Ghost Doctor

I can't choose either XD I'll follow your example ^^ Here are my recs for each genre:

RomCom: You Are My Hero

Medical: Dr. Romantic 2

Comedy: Yamato Nadeshiko Shichi Henge

Thriller/Investigation: Love Me If You Dare

Fantasy: Love and Redemption

Sports: To Fly With You

Military: Descendants of the Sun

Action: Save Me

Psychological: Move to Heaven + It's Okay to not Be Okay

Signal 

because it is literally the best :)