I like them all! I really have not one single character I like, because they all have traits that make them unique in their own special way. So for me, with this series anyway, I really don't feel right liking one character over another.
I cannot believe Yukine is hardly mentioned. Everybody comes to her for advice, and she's like everyone's big sister. She's the leader of not one, but two gangs, keeping them from going astray and she supports Tomoya and all the other main characters a lot. She literally rules the city. After that, it would Ushio. She's so fricking adorable.
Aiko (how can you hate him)
Tomoyo (thug life)
The girl in the illusionary world (or would she count s Ushio?)