I just love Si Jin! His looks, his smile, his personality, and his frank approach to love! Definitely someone I would date! Who doesn't wouldn't to know how the man in their life feels about them? 

Next would have to be Dr. Daniel! There are so many facets to his character I can't wait to see unfold! He has a sexy mysterious aura surrounding him.

Seo Dae Yeong and Kim Gi Bum: I like that in the beginning they made Gi Bum out to be some kind of rough around the edges 'gangster' kid, but then they show him crying and just in general acting a bit more childish since entering the army. Like, he had to grow up quickly (not to say he was mature but he was stealing, in a gang, etc.) and now he has the chance to live more like his age warrants. Though I suppose he still is rough around the edges ~

Dae Yeong because he seems like a good person but is perhaps a little emotionally stunted, so of course there will be a lot of character growth! It's interesting to see how he acts quite standoff-ish to even people he is close to, and to see how he acts based on what he thinks is right/wrong (how he chooses to do what he believes is the right thing even if it hurts him, and even how he chooses to do what he thinks is the right thing when it hurts other people, as long as he thinks it is the option that will hurt them least in the long run). And how he pretty much embodies the "cog in a machine" metaphor often used for soldiers; if he's told do something, he does it without verbal questioning. Like I said, I'm interested in how his character will grow.
My favourite so far has to be Lee Chi Hoon! I really like the way his character has a cute and funny side to him as well as a serious side when he is dealing with his patients. They also show a realistic reaction in episode 8 (Don't wanna spoil it just in case) and I'm always looking forward to whenever he's on the screen. Plus, it's Onew so cuteness overload!
My favorites couples are;
Song Joong Ki and Na Yeon
Dae YEong and Myung Ju
chi hoon Kim and his pregnant wife
i love them all...
Shi Jin is one of the best characters for me, he's like my ideal type - his personality won me over! lol >< And I really like Myung Joo too, she is so sure of what she wants and she goes after it, I admire her. 
Shi jin and doctor kang ♥