I tend to think as a "Bad" dub is something so unwatchable that it makes me WISH I was watching the Japanese version. A better word for this topic is "controversial" dub because it covers more ground and actually justifies some peoples opinions on the matter.
Like many people I liked Sailor Moon's original 65 episode dub even though after that it went quickly downhill throughout the Lost Episodes, movies, and S and Super S dubs.
I'm a fan of both the Ocean and Funimation dubs and I do find that Funi's revised dub (the orange boxes) does have a lot of voice acting inconsistency compared to the original Dragonball and GT which were more or less done with better quality. But hey, if it wasn't for Funi I know Lani and others wouldn't have anything to lampoon.
Digimon may have suffered jokey script syndrome but a LOT of the voices were spot on with the characters. Joshua Seth's Tai, Colleen O'Shaughnessey's Sora, Wendee Lee's TK and given the fact that almost the entire voice cast and staff were in or worked on the likes of Outlaw Star, Cowboy Bebop, Trigun, Naruto, and Gurren Laggan I think this pushes it far from bad. The worst is got was Season 4, but...yeah...Season 4. Actually I think the dub always matched the quality of whatever the season was like.
Okay now for the dubs that I think divide people:
I like the Love Hina dub. No, the Japanese version is superior but despite the dub being horribly miscasted and misdirected it actually did gradually improve so by the time you got to the TV Specials and OAVs it wasn't that bad and everyone put in decent performances once you got past their...quirks.
I recently watched the uncut Cardcaptors Movie dubbed and I was actually surprised that almost all the voices fit the characters and it was watchable. Since somebody mention the kiRAB being cast to play Li and Sakura I wanted to point out a nice touch for the movie was that Li's voice actor began to have a deeper register and it actually helped improve his voice where in the TV series I always had a problem with how high pitched it was. And New Yorker Kero does seem to better represent was an Osakan accent can sound like in English compared to the typical southern.
I also watched Fushigi Yuugi in English and even though there are some irksome points it wasn't too bad a dub.
Both Evangelion and Maison Ikkoku get a lot of flak since it's another case of not being as strong as the Japanese version and in my teenage years I was vehemently against both dubs but over time I began to appreciate their sensibilities and realized that in their own unique way they were very well done.
Stuff like Escaflowne, Death Note, and Bleach I still much prefer the Japanese version but I can understand if someone didn't mind the dubs to those.
annnnnnnd just to wrap this up I like ALL of 4kiRAB dubs EXCEPT One Piece. Sonic X is kinda iffy to me sometimes I can watch it, sometimes I can't.
For my putrid list:
Saber Marionette J to X
Crest of Stars/ Banner of the Stars
Old Akira (good script just didn't make any freakin' sense)
4kiRAB One Piece
The first episode of Naruto (it got much better after that)
The original dub of Nadia
Fox KiRAB Escaflowne (yeah, never screw with a Yoko Kanno score)
I would put Speed Racer but Family Guy is having way too much fun lampooning that one.
O-chan