Matsuri - easily my favorite Sola character. My liking towards Sola as a whole during the early stages can easily be attributed to her. Her interactions with Yorito made me like her even more. Never thought a character can be so teasingly playful yet unbelievably cute at the same time. Granted, i did like the early stage "my pace" Matsuri over the angsty and somewhat suicidal Matsuri in the end, but she easily remains as my favorite Sola character.
Mana - The friend you would kill to have. Despite the fact that her character development and background amount to a grand total of zero she is very likable and easy to sympathize with. Though her feeling towards Yorito remain under a question mark for the better part of the series, i guess it is safe to say she liked(loved?) him. The fact that she tried to push Matsuri and Yorito together despite this makes her gain even more points.
Mayuko - loved her interactions with Takeshi. A tragic yet amusing character with poor fashion sense. Whats not to like ?
Thats about it for my favorite list.