Hmmm. I like Dao Min Si because he is believable. He has a true development throughout both seasons, a veritable growth as a person, and I like Shan Cai too for the same reason. She isn't by far a perfect character: she starts as obnoxious, albeit brave, and learns to be a gentler person, but she also stays consistent to her character, a fighter. Like goldenseal writes, their love story is sweeter - and I would add more passionate - than elsewhere. I ended up liking them as a couple, and this is why I didn't root for Vic's character: not because he isn't likable, on the contrary, but simply because he wasn't a good match for Shan Cai, in my opinion.
This said, even the interaction between the 4 friends is better explored here. I may be mixing a little the 2 seasons now, since I watched both a couple of years ago, but I grew very fond of Vanness's character too, and his love story (something which is completely missing in any other version).
In conclusion, my favourite characters would be the main couple. I also loved how they "fight" against Dao Min Si's mother - enough said! ;)