It's a toss up between 4.... I can never decided which one is my absolute number one favourite, but I usually say which one I enjoy most at the time.
At the moment my favourite manga is Yami no Matsuei. It's great, it's got everything I love in a manga.... drama, angst, comedy, magic, and bisshies with puppy ears ^___^
Yami is closely followed by Angel Sanctuary, X and Tokyo Babylon.
Sense a pattern here