Weeeeell... I've only watched Cowboy Bebop, Elfen Lied, Samurai 7, and Samurai Champloo. Other than that, only seen snippets of Naruto, Inuyasha, and Dragonball... So, out of those, yeah I'd say Cowboy Bebop is #1. And I can't imagine watching an anime I like more.
The story is good. The characters are believable. It brings an unprecedented authenticity to space anime. And the music is AMAZING.
Not many animes could top all of that.