in terms of anime dubs, the best that I know of from Ocean would have to be Ranma 1/2. Most of the their actors we're properly trained, and while the anime had a shaky start, things progressively got better and they ended up continuing with a full-budget adaptation of Inuyasha.
The worst that I've heard would have to be Slayers. It's actually difficult for me to watch because of the amatuer voices. Lisa Ortiz was pretty much the peak of talent for the first series (as well as that guy who did Gourry, who's also the voice of Brock from PKMN). But i did hear from fans that about 20 or so episodes in they made some significant changes to the cast.
The worst that I've heard would have to be Slayers. It's actually difficult for me to watch because of the amatuer voices. Lisa Ortiz was pretty much the peak of talent for the first series (as well as that guy who did Gourry, who's also the voice of Brock from PKMN). But i did hear from fans that about 20 or so episodes in they made some significant changes to the cast.