I agree that Angel was better, much darker. Second season Angel is among the best of TV, and I think one of the writers was the guy who does the Shield now. Firefly also had some amazing episodes, but never really had the chance to fully grow. It didn't get a full season, and when the episodes were originally shown they were shown out of order. I think they only ended up showing about 9 of the 14 episodes, and they also wouldn't let him use the original two-hour pilot, but made him rewrite it into a mediocre (comparatively) one-hour train heist episode. I was pretty sad Serenity didn't catch on, I don't know that it met the potential the show had, but it was a good movie.
4th Season Buffy was by far the weakest in my opinion, so I would suggest anybody starting out does not catch that one. Reruns may be dangerous for this reason... I would suggest starting with the first three seasons, and maybe 5 or 6 (who else thought the musical episode was brilliant?). They actually just rereleased all the Buffy seasons in slimmer cases and for a cheaper price (I think they're at around $27.99 right now) in the U.S. yesterday, like they did with X-Files a little bit ago. Angel will probably follow soon. They had a box-set of the entire show that was pretty cheap, but it's out of print now. I think he's working on the "Wonder Woman" movie right now. Here's a decent source of information on his happenings:
http://whedonesque.com/