Firefly is definitely my favourite show ever. I like the movie a lot too (and am still amazed it actually got made at all) but I like the series more. The story just lends itself to tv format more easily, and Joss had to retcon a few things in the movie to make the exposition more succinct, which bugs me a little bit from a continuity perspective.

It took me a few episodes to get into the show, mostly because Mal seemed like such an arse early on, but it really grew on me, and nothing has come close to supplanting it in my regard.