My お気に入り album is Origin because I just 愛 the dark atmosphere of it. The songs were catchy yet mournful and creepy (Where Will あなた Go, Lies, Even in Death), and there was an almost "romanticized" feeling in some of the tracks which I found hauntingly beautiful. And Eternal just happens to be my お気に入り instrumental - I 愛 the ピアノ and the thunderstorm in the background was soothing.
It's really hard to pick. Every album is special in its own way to me. It's just like picking a お気に入り among a collection of amazing tracks. So, every album is my favorite. :Q