I'm a librarian who loves anime, manga, and reading a wide variety of genres.
The original post is here.
I've noticed that there are patterns to the sorts of characters I can think of for certain letters. "M" and "S" are heavy in characters I consider true favorites. "J," on the other hand, is heavy in characters who I neither like nor dislike (Jaenelle from Anne Bishop's Black Jewels series), characters I'm not fond of (Jason from Laurell K. Hamilton's Anita Blake series), or characters I flat out hate (Joffrey from George R.R. Martin's Song of Ice and Fire books).
The best I can come up with is Jade from Martha Wells' Raksura books. I've only read The Cloud Roads, and that was long enough ago that I'm having trouble remembering specifics, but I remember enjoying her and Moon's romantic subplot. Which I realize isn't really the same thing as liking the character. Hmm. Maybe I should choose Jaenelle instead? (Nah.)