I like most anything by Osamu Tezuka, as well as the manga Pluto (which is based off of a famous Astro Boy arc).
Generally speaking, I prefer manga over anime - anime takes me longer to get through, because with manga I can get through an episode's worth in about five minutes, whereas for anime I have to wait for the episode to do things. There are some exceptions, though: Outlaw Star's anime is far superior to its source manga, and Metropolis is a better movie than a manga (sorry Tezuka, but provided even you didn't like the manga, I think that this is justified!).