Dragon Ball Z by a long shot. Don't listen to what Narutards say: Naruto isn't a very good anime. Believe it!
Naruto is one of the best anime out today. Its been going strong for like 10 years! And there still putting out new episodes.
For those who haven't seen it, it only takes a few episodes to get you hooked. The character developement is amazing, its been out for so long you basicaly witness all of them grow up from children to adulthood. The stories will have you breaking night to see what happens next, Masashi Kishimoto is a talented writer and has done a great job with this story. The only bad thing I can say is that around episode 50 or so, they started airing a lot of filler episodes that deviated from the main plot, like little sub-stories, you may like them though. When they get to Naruto Shippuden, they pretty much stick to the script, which is based off the manga chapters, the meat and potatoes of the story.
Don't believe this guy who says Naruto isn't a good anime, bad animes don't last as long as this one has. Give it a try for yourself, your probably going to love it.
Also check out Bleach, History's Strongest Desiple Kenichi, Baki the Grappler, Death Note, Trigun, Chrome Shelled Regios, Full Metal Alchemist, Fate/Stay Night, etc... Some of these only have one season, but the stories don't end there, you can continue to follow by reading their manga chapters that are released, usually once a week. Some good mangas are; The Breaker, Gamaron, Holyland, and Veritas(ended kind of stupid, think the writer had some issues with his company at the end).
One other thing I forgot to mention, try to watch these in their original language with English subs. The English dubbed versions don't do them any justice, they loose a lot of their emotion, humor, and edginess.