A note from Gjallarhorn: We get one of these "What is your favorite anime/manga?" threads once every two months or so, which then sinks into the abyss and is replaced by another. I'm putting a knife in the back of this pattern, and stickying this thread as the "official" version of the thread.
It's a difficult one for me.
I would have to say either Code Geass or Bleach.
Kuroshitsuji was pretty good, too.
p.s. if there's been a thread like this before I'm sorry.