---Dragon Ball Z--- You should choose Dragon Ball Z because at the beginning of the story, one power level is Over 1000, while I bet Avatar would only have 5. And at the middle of the series, the power levels are WWWWWWAAAAAAAAYYYYYY OVER 9000. I've read that at the end, Aang at his best, in Avatar State, doesn't even break 1000. Imagine Vegeta against Zuko and Goku wouldn't have to lift a finger. Can't Goku easily destroy a planet? Vegeta would just use Galick Gun or Big Bang Attack, and he might accidently destroy Earth. Then Broly against everybody in Avatar combined, Broly would still win. Remember, Broly can destroy a GALAXY. That's better than Goku. Krillin versus Toph. Krillin would easily win. That's why you should choose Dragon Ball Z. ---Why You Should Choose Avatar--- I don't see any reason to choose Avatar...
