I think City Hunter is the best revenge drama. It's not one of my favorite genres because when it is done badly, it's really bad. But City Hunter is unique in the genre in that it is very thoughtful in regards to the revenge and also it has the best villain because they actually make you feel some sympathy towards him. I also enjoyed Equator Man for the most part, although it had its issues. But the acting was really good and it was very beautiful to look at. Innocent Man too because it is very different than other revenge dramas I've seen, and because of Song Joong Ki (enough said).
I'd avoid A Man Called God and Temptation of an Angel. They are terrible (and even more so because of how their awfulness brings down the great Song Il Kook and Bae Soo Bin, respectively).
Bad Guy (don't watch if you're endings lover).
Temptation of a wife and Temptation of an angel but those two dramas are really long. However, they contain a great revenge plot.
A love to kill (melodramatic)
If you're looking for a strong revenge plot, I would not recommand Innocent Man, it does sound like revenge but it's really not.
Tree with deep root
The Baker King (im not sure i forgot)
Giant >>> the best but Long
The Equator Man
Time B/w Dog and Wolf
Little Girl K
A Man's Story
The Chaser (i think)
Nice Guy (i think)
Little Girl K is best in revenge in my view...
City Hunter - Great
Bridal Mask - So so
Innocent Man - O.o
Glass Mask....I watched up-to ep 9 and its very good.
Yellow Boots....I watched around 20 something and I loved it. On-hold because not fully subbed.
And I heard Pink Lipstick and Temptation of Wife are great...
A Love To Kill
I'm Sorry I Love You
Story of a Man
Swallow the Sun
Temptation Of An Angel
The Princess's Man
Time Between Dog And Wolf
Also Queen of the Game and A Man Called God but I didn't wach them yet.