Sailor Moon...dear god it's horrid. And I'm not talking about the little insignificant changes that everyone likes to bitch about (ie, calling them "Scouts" instead of "Soldiers", attack names, ect.)...I mean, making a lesbian couple go by the role of "cousins" and yet...leaving all their affectionate scenes in was really, really strange. They never kept their own story straight (a la, calling Ami "Amy Mizuno" and episodes later calling her "Amy Anderson", making Sailor Mercury become the second "scout" but then making Mars
specifically say later on "no way, I was a scout before you!")...it was butchered, and while in the first two seasons (DiC's editing) was done well enough that an unknowing person couldn't tell what was cut and changed, the second two seasons (Cloverway's editing) were so badly done it was painfully obvious when cuts, mostly pointless cuts, were made. Not to mention that in the second two seasons they had people who couldn't voice act worth a crap.
But eh, for me it would be:
#5:
X the Movie - It was just bad.
#4:
Neon Genesis Evangelion (Original Dub) - I have yet to see the Platinum version, but the original dub I just couldn't get through the first three episodes.
#3:
Those Who Hunt Elves - Again, I couldn't make it though more than a few episodes, where as I loved it subbed.
#2:
Tenchi - It didn't even make sense by the time they were finished editing it, and Tenchi's voice actor just plain sucked.
#1:
Sailor Moon (Particularly S and Super S) - For reasons stated above, and many many more which can be found at
www.smuncensored.com.
I generally dislike dubs though. The only two anime I can think of that I actually prefer dubbed are "Street Fighter II: The Animated Movie" and "Akira".