I choose all of them
How are you going to make a girl choose between So Ji Sub amd Gong Yoo?!?! I can't, sorry! LOL!
they are all my favorite, but I watch more drama with Ji Sung than anyone else, so JI SUNG !! 
This is very easy:

SO JI SUB! 
Most charming, most good looking, best acting and those deep genuine heart-melting eyes!  
1. Lee Dong wook
2. Gong Yoo

so hard thought XD 
2nd place:  Park Hae Jin and Lee Dong Wook 
3rd place:   Lee Joon Gi

The rest of the men mentioned are meh 
i pick one for cute favorite actor :park seo joon
i pick one for sexy favorite actor : so ji sub
i pick one for charismatic favorite actor : lee min ho
i pick one for ahjusshi favorite actor lee dong wook
Ji Sung all day!!!

And all the rest a close 2nd except LMH.