Ruro: In no particular order, after Aya it's Remilia, Yuyuko, Kaguya, Nitori, Kanako, Utsuho, Renko, Torohime no Watatsuki, Reimu and Marisa.
(EDIT: I also have to give honorable mentions to Rin Satsuki, Wriggle Nightbug and Cirno. My esteem for Yukari is growing, too, and I have to give props to Byakuren for her backstory. But the ones I mentioned first are in the top tier, and likely always will be.)
The others I like, too, just not as much. There's only one I could do with less of, and even then I can't say I dislike the lil double-tailed spazzo.