See seemed to be one of the most interesting characters IMO, being shy and scarred. I'm hoping to be a detailed back story so I can have some idea of why she's the way she is. I just go the game and I just made it to Act 2 and so far, I'm having fun.
This will be my second VN, first one being Tsukihime.
Rin was definitely my favorite path. As a character I found her to be the most intriguing (gotta love short hair, too). And getting a good end for her was the most rewarding since her path took the most time and there were so many up's and down's throughout her storyline. It felt like more work was put into her path than the other characters since you were actually able to see her artwork.
Her path was also the one that made me cry the most. Not that I didn't cry for every path. Even Kenji's end, I laughed until I cried :D
tl;dr: 100% in the game, Rin is the best. (Hanako second, so cute)
I feel like Emi was the "right" choice, like if KS were an anime, she would be the main heroine. I should probably play the other routes first, though.