I don't know! There are so many good ones and I think it is constantly changing for me. The following are some of my प्रिय in lyrics, sound, and visual.
"Key" द्वारा Daisuke Ono (Psychic Detective Yakumo) "Nirvana" द्वारा Mucc (Inu X Boku SS) "World's End" द्वारा Flow (Code Geass) "Spell" द्वारा LAMA (NO.6) "Closer" द्वारा Inoue Joe (Naruto Shippuden) "Things I can do" द्वारा HOW MERRY MERRY (Natusme Yuujinchou) "Stray" द्वारा Steve Conte (Wolf's Rain) "Zero!!" द्वारा Minami Kuribayashi (The Devil is a Part-timer!)
But I'll go with "Izayoi Namida [Hesitating Moon]" द्वारा Yoshioka Aika (Hakuouki) because I could just listen to it over and over again. And I प्यार the lyrics! It basically means time is fleeting and फूल don't last forever. But spring always comes and the cycle of life will continue again.