The worst anime I've ever seen is the sonic the hedgehog anime. Not Sonic X, the one they made before that, in 1999 or so. I really liked the music, too bad everything else about it sucked.
I, for one, liked Dragonball GT a lot more than Dragonball Z. It's definitely far from my favorite, but still better than the series before it. (And I don't mean the crap dub funimation did. I mean the original version of dragonball GT.) The reason is because it gets to the point a lot faster. Most fights in the series lasted considerably less than an episode, around 5 minutes or so. I think the longest one in the entire series is maybe 3 episodes. None of the 5 minutes of story taking 5 episodes crap. That, and the series size was much more managable - 64 episodes for the entire series.