Definitely Bebop, an absolute classic, although (like many, many people in this thread) I liked Champloo too.
Wtf is with the people that say they only saw one of the two series..? Why are they posting in a thread which has a requirement of having watched both? Man, some people...
Also in regards to the whole thing about Spike dying so easily at the end, IMO I think he DID die, and it's because he no longer had any more connections to his past. The love of his life died and he got revenge on the one who did it. Sure, there's still Faye and Jet, but it seemed like they meant almost nothing compared to Julia.