My favorite Manga is definetly... umm well... actually i have three favorites.
In no particular order:
1) Ichi the Killer (Sick and twisted, yet amazing artwork and plot.)
2) Yakitate Japan (Heh, a manga about baking. But don't let the main idea fool you, it actually a amazing and hilarious manga. And what other manga features a bagel so good it makes you go to heaven...?)
3) Pretty Face (It's main idea is perverted, but it's a hilarious, it's plot is intense and it has lot of cute girls and boys in it... ^^)