Ji Sung is currently my favorite! Love his performance is Kill Me Heal Me, Secret, and Protect the Boss... He deserves an award for Kill Me Heal Me.

Then
Joo Won- Love his acting in Good Doctor
Song Joong Ki- He did an amazing job in Innocent Man, Werewolf Boy and Penny Pinchers
Jang Hyuk- Loved him in Fated to Love you... my favorite Drama... he's hilarious!
Kim Soo Hyun- Although he isn't in my top dramas, his acting is so diverse (Dream High, You Who Came From the Star and Producers)

Oh and I'm currently watch Fall for Innocence and I'm digging Jung Kyung Ho's acting
Ji Sung - I love his acting skills and I'm always looking for his new series. The best on my list when it comes what roles he picks, how he plays and how versatile he is as an actor, but saying that...

Kang Ji Hwan - one role that is stuck in my head and how much Chemistry he has on screen in LIe to Me series. He still plays good in other dramas, but Lie to me is it for me when it comes to KJH.

Lee Min Ho - perhaps not as talented actor as others there but his smile is a killer. There is something about him that I like in most of the dramas. Personal Taste and City Hunter are my best for me. 

Hyun Bin - Secret Garden was great. He is very handsome as a person as well very good actor. He also is one of those actors who don't disappoint the same as Ji Sung.

Lee Dong-wook - Loved him in Scent of a Woman and Hotel King. I love the mystery face I call him. He looks so calm, and is a great actor. For me he looks very intellectual. 

Jeong Jinwoon - people think I am crazy to pick him. He did not play in too many dramas. Yes... but I liked him in Marriage not Dating. He has a gorgeous face and smile that brightens the screen. I find him very handsome because of that.

Jo In Sung - I only liked him in That winter, the Wind Blow and It's OK that's Love. Otherwise he is 50/50 for me. 

Yeon Woo-jin - I like him In Marriage Not Dating, and now watching Divorce Lawyer in Love. What I like is the fact his facial expressions are entertaining, he is adorable actor. Unique in some ways because of his gestures and how he acts. I kind of like him playing different roles lately. 

Jung Yong Hwa - Great singer! Good actor! Not a crazy fun, but I like him in many roles. He played very well in Three Musketeers and I like his role in You Are Beautiful. Love him singing in dramas too.  
Lee Min Ki - I loved his films Very Ordinary Couple and Spellbound and after that im resisting watching all of his discography bc he is in army now :(

Yoo Ah In - fell in love with him in Secret Love Affair

Kim Jae Wook - Im still waiting for him to cast as lead male and get the girl xD

Joo Won - He was brilliant in Good Doctor so im excited for his new drama
Lee Sung-min and Lee Sun-kyun
they are many but mostly kang ji kwan
MY TOP 5:
Kim Soo Hyun
Seo In Guk
Ji Chang Wook
Lee Min Ho
Park Bo Gum
Gong Yoo
Ji Sung
Park Yoo Chun
Ji Chang Wook
Jo in sung: Perfect acting and so cute and handsome oppa, especially in It's OK that's love.

So ji sub: Great actor good looking oppa, I love his character in Always and the master's sun.

and I also enjoy lee min ho and kim soo hyun's acting.
Kim Bum
Lee Dong Wook
Kang Ha Neul
So Ji Sub
Joo Sang Wook
Kwon Sang Woo
Jo Seung Woo
Park Hyung Shik
Hoya
Park Yoo Chun
Lee Dong Wook
Cha Seung Won
Ji Chang Wook
lee min ho  (the heirs)
Ji sung (kill me heal me)
lee jong gi (scholar who walk the night )
Lee Won Geun (sassy go go)

Ji Chang Wook
Kim Soo Hyun
Seo In Guk
Lee Dong Wook
Hyun Bin
Joo Won
Seo In Guk
Ji Sung
Lee Jong Suk
Kim Soo hyun
Kim Woo Bin
Jo In Sung
Jang Hyuk
Joo won
ji chang wook
The very best actor for me is Lee Kwang Soo! 

He's hilarious and really amazing when he acts! He puts his heart and all in acting